Has this ever happened to you? You're using Teams like normal and one day it doesn't start. No reason, just the usual Teams error that tells you nothing. You try the usual workarounds (Mark Vale's write-up on cleaning the Teams Cache is invaluable) but nothing helps. So back to that error that doesn't tell you anything.
Or maybe it does tell you something. The error code in the bottom left corner: CAA70007. That looks promising... except it isn't. No sign of the error in the Microsoft documentation and no help in the Microsoft Answers.
But I've found a possible answer. To see if you have the same issue I was having, open up your Event Viewer, and expand Applications and Services Log > Microsoft > Windows > AAD, then click on the Operational Log. If you see a lot of 1098 AADTokenBrokerPlugin errors, then I may have a solution.
For me, there was a series of 0xCAA5001C Token Broker Operation Failed errors. This can indicate things like out of date components, faulty internet connection, etc but if you're reading this you've probably already checked all that.
Searching for more info about 0xCAA5001 errors then led to this Microsoft article which is a useful fix.
You should read and understand the article before making changes but If you're in a rush and just want a short answer that doesn't involve more reading then, what I did was as follows: (the usual warnings about registry editing apply)
- Open regedit and browse to the following key:
HKEY_CURRENT_USER\Software\Classes\Local Settings\Software\Microsoft\Windows\CurrentVersion\AppModel\SystemAppData\ Microsoft.AAD.BrokerPlugin_cw5n1h2txyewy
- Right click, select permissions and disabled inheritance on this key(making sure to create a copy of the current permissions when asked).
- Still in the permissions window, I then re-enabled inheritance, ticked Replace all child objects permission entries with inheritable permission entries from this object and hit OK. This fixed my issue.
Teams now starts. Hooray! I do love Teams as a concept but issues like this make me think there's a lot of work to be done on the basic tools.