Microsoft Teams Error Code 0xCAA90018 usually appears when the Windows sign-in identity on the device does not line up with the Microsoft 365 account that Teams expects to use. Microsoft’s own status table describes this code as a credential mismatch, not a generic connectivity failure. That detail matters, because the fix is rarely “reinstall and hope.” It usually sits in account selection, saved credentials, Windows account binding, or old Teams cache data. Microsoft also says Teams serves over 320 million monthly active users, so these identity-flow issues surface in many real Windows environments, especially on devices that switch between personal and work accounts. [✅Source-1]
What the code points to: Teams is reaching the sign-in stage, but the credential set in Windows does not match the Microsoft 365 work or school identity that the app needs. When that happens, the app can loop, reject the password, or return to the sign-in screen after you think authentication finished.
Table of Contents
What The Code Means
Microsoft lists 0xCAA90018 as: “You’re not using the right credentials.” The wording is short, but the fuller explanation is more useful: the Windows credentials you signed in with are different from your Microsoft 365 credentials. This pattern appears in several documented Microsoft Teams error codes where the desktop client reuses an outdated identity context. Teams also uses modern authentication, so a stale sign-in state in Windows can break the handshake even when the account itself is valid. That is why the same password may work on the web and still fail inside the desktop app. [✅Source-2]
Often, it is not the password alone. The real break happens between Windows, cached tokens, and the account that Teams tries to pick up automatically. On machines used for both personal and work activity, that gap appears more often. Quietly, then, the wrong identity gets reused.
Where The Mismatch Starts
Common User-Side Triggers
- A different account is signed into Windows than the one Teams should use.
- The account password changed, but old credentials still sit in the device cache.
- The device was connected to one work tenant before and now needs another.
- Teams desktop is trying to reuse a saved identity from a previous session.
- A personal Microsoft account and a work account are both present, and the wrong one is selected first.
What Teams Sign-In Depends On
- Modern authentication behavior in Windows.
- Whether the device already knows the right work or school account.
- Whether single-factor or MFA is in play.
- Whether the desktop client can reuse a valid local sign-in state.
Microsoft explains that Teams sign-in behavior changes with Windows, MFA, and the organization’s identity setup. [✅Source-3]
Fix Order That Usually Works
Do these steps in order. That keeps you from wiping useful sign-in state too early. A lot of users jump straight to reinstalling Teams; usually, that burns time and leaves the same account mismatch behind.
- Confirm the exact account that should open Teams. Use the full work or school email address, not an alias you only use for mail routing.
- Sign out of Teams fully and sign in again with that exact work or school identity.
- Test the same account outside the desktop app. If it opens in the Microsoft work account portal, your account is usually fine and the desktop device state becomes the main suspect.
- Check the Windows account binding. In many cases the device is not connected to the correct work or school account anymore, or it is connected to an older tenant.
- Remove stale saved credentials so Teams cannot silently reuse them.
- Clear the Teams cache with the right path for the client version you use.
- Only then move to device-level or admin-level checks such as service health, Conditional Access, licensing, or account policy.
1) Test the Account Outside Teams
Open the My Account portal for the same work or school identity. Microsoft says this portal lets users manage security info, devices, and sign-in activity. If that account opens there but not in the Teams desktop client, the evidence shifts toward a local Windows or client-state issue, not a dead account. [✅Source-4]
A useful split: if the account fails in both the portal and Teams, look at the account itself. If the portal works and only the desktop app fails, look at the device’s saved sign-in state.
2) Check Windows Account Binding
Windows can hold personal, work, and app-only accounts at the same time. Microsoft’s Windows account guidance shows that you can connect or disconnect a work or school account under Settings > Accounts > Access work or school. If the wrong tenant is connected, or an older connection is still there, Teams may try to authenticate with the wrong identity context. Disconnecting the stale entry and reconnecting the correct work account fixes many stubborn cases. [✅Source-5]
3) Remove Saved Credentials That Teams Keeps Reusing
Windows Credential Manager stores sign-in data for websites, connected apps, and networks. That matters here. If Teams keeps picking up the wrong cached credential, remove the related saved entries from Web Credentials or Windows Credentials, then start the sign-in flow again. Old entries after a password change are a classic source of repeat failures. [✅Source-6]
4) Clear The Right Teams Cache
Microsoft documents different cache locations for Classic Teams and New Teams. That distinction matters. Clearing the wrong folder leaves the real sign-in residue in place. Microsoft’s official Windows paths are:
- Classic Teams: %appdata%\Microsoft\Teams
- New Teams: %userprofile%\appdata\local\Packages\MSTeams_8wekyb3d8bbwe\LocalCache\Microsoft\MSTeams
Microsoft also notes that the first restart after cache removal can take longer because the app has to rebuild those files. That delay is normal. [✅Source-7]
Do not skip the full quit step. If Teams is still running in the tray, cache files can stay locked and the cleanup becomes incomplete.
How To Tell Whether The Issue Is Local or Tenant-Side
| What You See | What It Usually Points To | What To Do Next |
|---|---|---|
| Teams desktop fails, but the same work account opens on the web | Local device state, stale credentials, or cache | Check Windows account binding, Credential Manager, then clear the correct Teams cache |
| Teams desktop and web both fail | Account, password, policy, tenant, or service issue | Verify the account in the My Account portal and send the error with time stamp to IT |
| The device used to belong to another tenant or user | Residual work-account connection on the device | Review Access work or school and remove stale entries |
| Only one machine fails while another machine signs in | Machine-specific sign-in state | Clean saved credentials and Teams cache on the failing device |
| Many users fail at the same time | Service-side incident or organization policy problem | Check Microsoft 365 service health before deeper local cleanup |
That last row matters. Microsoft says admins can check service health in the Microsoft 365 admin center, and there is also a public service status page for issues that can block tenant sign-in. If multiple users hit the same barrier at once, stop treating it as a single-device repair. [✅Source-8]
Technical Checks On Windows
This error is mainly an identity problem, but a broken client environment can make that identity flow fail or loop. Microsoft’s published Teams client requirements for Windows include Windows 10 version 10.0.19041 or higher, 4 GB RAM, 3 GB available disk space, and an up-to-date WebView2 component. If the sign-in window behaves oddly, verifying those basics is worth the minute it takes. [✅Source-9]
Checks Worth Doing
- Make sure the machine date and time are correct.
- Confirm you are entering the licensed work or school account, not a personal Microsoft account.
- Quit Teams from the tray before any cleanup.
- Restart Windows after removing old credentials and cache.
- Try Teams on the web before reinstalling the desktop app.
When Reinstalling Actually Makes Sense
- The client files are damaged.
- The sign-in window does not render correctly.
- The app crashes before authentication starts.
- You already cleared the right cache and removed stale credentials.
Reinstalling is a late step here, not the first one.
What To Send To IT If The Error Stays
When this issue reaches admin hands, vague notes slow everything down. Send a short, clean report.
- The exact code: 0xCAA90018
- The full work or school email you used
- Whether the same account works in the My Account portal or Teams on the web
- Whether the device is connected under Access work or school
- Whether you removed related entries from Credential Manager
- Whether you cleared Classic Teams or New Teams cache
- The approximate local time of the failed sign-in
- Whether other users in the same organization are affected
That small list saves back-and-forth. It tells IT whether they should look at the device, the user object, tenant policy, or a wider Microsoft 365 incident.
FAQ
Does 0xCAA90018 always mean the password is wrong?
No. It often means the wrong credential context is being reused on the device. The password may be correct, while Windows or Teams is still trying to sign in with an older or different account state.
Why does Teams on the web work while the desktop app fails?
That pattern usually points to a local desktop issue such as stale cache, saved credentials, or an outdated work-account binding in Windows.
Should I remove my work account from Windows?
Only if you confirm that the device is linked to the wrong or outdated work account. Removing the stale connection and then adding the correct one is often cleaner than leaving both states in place.
Is clearing cache enough on its own?
Sometimes, yes. Still, if old credentials remain in Credential Manager or the wrong work account is connected in Windows, cache cleanup alone may not stop the loop.
When should I stop troubleshooting and contact IT?
Do it after you confirm the right account, test web sign-in, review Access work or school, remove saved credentials, and clear the correct Teams cache. Contact IT sooner if several users are affected at the same time.