How to Fix Microsoft Teams Error Code CAA50021 "We Couldn't Sign You In"
dsregcmd /leave. Full steps below.What "Error CAA50021" means
When you sign in to Microsoft Teams, it doesn't ask for your password every time — it stores authentication tokens (small digital keys) on your PC and quietly refreshes them in the background. Error CAA50021 is what you get when that refresh process breaks down: Teams tries again and again to get a fresh token and fails every time. Microsoft's server-side message behind the code is "number of retry attempts exceeds expectation," which is a formal way of saying the sign-in loop gave up.
The most common trigger is a password change or an account recovery: your old tokens stop working, but Teams and Windows keep serving them up anyway, so every sign-in attempt dies on stale credentials. It can also come from a damaged Teams cache, a broken device registration with Microsoft Entra ID (formerly Azure AD), or an outdated Teams build whose sign-in components no longer talk to Microsoft's servers correctly. Because the problem is almost always local to your device — not with Teams' servers — the fixes below work through your cached data, your saved credentials, and your device registration in that order.
Common causes
- Corrupted or expired cached sign-in tokens: Teams keeps retrying with bad tokens until it gives up with CAA50021, most often right after a password change.
- Stale Office credentials in Credential Manager: Windows stores old Office credentials that conflict with the new ones Teams needs to sign in.
- Broken device registration: the PC's registration record with Microsoft Entra ID is damaged or out of sync, so token requests are rejected.
- Outdated Teams or WebView2: an old Teams build or a broken WebView2 runtime — which powers the sign-in screens — can fail the token handshake entirely.
- Conflicting work or school account connections: duplicate or half-connected work accounts under Settings > Accounts > Access work or school confuse the sign-in process.
How to fix "Error CAA50021" — step by step
Work through these fixes in order. Steps 1 and 2 resolve this error for most people.
- Quit Teams completely and clear its cached data. Right-click the Teams icon in the taskbar corner and choose Quit — if you skip this, locked files will stop the cleanup. Then press Win + R, type
%appdata%\Microsoft\Teams, and press Enter. Delete everything inside the folder (not the folder itself). This wipes the corrupted sign-in tokens and forces Teams to rebuild its authentication data from scratch. Restart Teams and try signing in — for many people, the error is gone right here. - Delete stale Office credentials from Credential Manager. Clearing the cache removes Teams' copy of the tokens, but Windows keeps its own copy. Open Start, type Credential Manager, and open it. Switch to the Windows Credentials tab and remove every entry that starts with
MicrosoftOffice16, plus any generic credentials mentioning MicrosoftAccount or MSTeams. Then restart your PC — not just Teams — and sign in again. With the old credentials gone, Teams gets a genuinely fresh set and the retry loop ends. - Leave and re-join the device registration. If the sign-in still fails, the device's registration with Microsoft Entra ID itself may be the problem. Press Win + R, type
cmd, and rundsregcmd /leave— this detaches the PC from its old, possibly damaged registration. Then open Settings, go to Accounts, then Access work or school, select your work or school account, and choose Disconnect. Restart the PC, go back to the same page, reconnect the account, and sign in to Teams. Windows will register the device cleanly this time. - Fix the system clock, then update Teams and WebView2. Token validation is time-sensitive: if your PC's clock is off, valid tokens look expired and every refresh attempt fails. Right-click the taskbar clock, choose Adjust date and time, and make sure Set time automatically is switched on. Then open Teams, click your profile picture, and choose Check for updates. If CAA50021 persists, the sign-in screens themselves may be broken — repair or reinstall the Microsoft Edge WebView2 Runtime (find it in Settings > Apps > Installed apps, click the three dots, and choose Modify), then retry sign-in.
- Temporarily disable VPN or proxy, and confirm your license. A VPN or corporate proxy can intercept the repeated sign-in requests Teams sends and corrupt the token exchange — disconnect from any VPN, go to Settings > Network & internet > Proxy, and switch off any manual proxy setup, then try signing in again. Also, if this is a company or school account, confirm that a Microsoft 365 license including Teams is actually assigned to you — unlicensed accounts can fail sign-in with the same error code, and only your admin can fix that.
- Use the Teams web app meanwhile, or ask your IT admin. If your PC is managed by your company or school and the error survives all five steps, the broken piece is likely your device's record in Microsoft Entra ID — and only an admin can reset it. Tell your IT department the error code and which steps you already tried; they can check the device record and re-enable registration from their side. Meanwhile, you don't have to miss your meetings: open Chrome or Edge and go to teams.microsoft.com. The web app signs in through a different path and usually works even when the desktop app refuses.
Did this fix it? Quick checklist
- Teams signs in without the CAA50021 error
- No old MicrosoftOffice16 or MicrosoftAccount credentials remain in Credential Manager
- The device is registered cleanly with Entra ID (run
dsregcmd /statusin Command Prompt to check) - Your Windows clock is correct and Teams plus WebView2 are up to date
If you've done all six steps and CAA50021 still appears, the issue is above your device: your IT admin may need to remove and re-add your device record in Microsoft Entra ID, or your account may be missing its Microsoft 365 license. Try signing in on a different device — if it works there, the block is specific to this PC's registration; if it fails everywhere, the problem is the account itself and only your admin can clear it.
Frequently asked questions
What does Teams error code CAA50021 mean?
CAA50021 means Microsoft Teams tried to refresh its sign-in tokens and failed repeatedly — Microsoft's own message behind the code is "number of retry attempts exceeds expectation." In practice it means the saved login data Teams relies on is stale or corrupted, so sign-in cannot complete and you are locked out of the app.
Why does CAA50021 appear after I change my password?
A password change is the most common trigger: Teams keeps trying to use its old cached tokens after the password changes, and Windows Credential Manager still holds the old Office credentials. Every retry fails, and after enough failures Teams gives up with CAA50021. Clearing the Teams cache and deleting the stale credentials is the fix that addresses this directly.
Will clearing the Teams cache delete my chats?
No. Your chats, teams, and files live on Microsoft's servers, not in the local cache folder — deleting it only removes temporary sign-in data and UI leftovers. When you sign back in, everything re-syncs. The one thing you may need to redo is signing in to your accounts and re-pinning any custom chat order, which returns automatically as data syncs.
Do I need my IT admin to fix CAA50021?
Usually not — the cache and credential steps fix it for most personal and unmanaged devices. But if the PC is company-managed and the error survives all the local fixes, the device record in Microsoft Entra ID may be the problem, and only an admin can reset it. If you also see licensing errors, your admin needs to confirm your Microsoft 365 license first.