Outlook won't sign in and shows "Something went wrong" with error tag 657rx. This happens when cached Azure AD or work/school account credentials get corrupted or conflict with each other. This error also appears as 0x8004dec5, error code 1200, or CAA50021 in different Microsoft apps.
The Fix
Same Error, Different Codes
These are all the same authentication cache issue:
- 657rx - Outlook/Teams error tag
- 0x8004dec5 - Windows error code
- 1200 - Azure AD error code
- CAA50021 - Teams-specific code
The fix is identical for all variants.
Open Settings and disconnect any stale work or school accounts:
Settings > Accounts > Access work or school
Look for any accounts listed and click Disconnect on each one.
Then clear the cached identity folders. Close all Office apps first:
# Close all Office apps, then run:
Remove-Item "$env:LOCALAPPDATA\Microsoft\OneAuth" -Recurse -Force -ErrorAction SilentlyContinue
Remove-Item "$env:LOCALAPPDATA\Microsoft\IdentityCache" -Recurse -Force -ErrorAction SilentlyContinue
Restart your PC and relaunch Outlook. Sign in fresh when prompted.
Verify
Outlook should launch and prompt for credentials. After signing in, the error shouldn't return.
If it persists, run an Online Repair:
Control Panel > Programs > Programs and Features > Microsoft 365 > Change > Online Repair
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