Hi Cripken2,
About the sign-in error, do you mean the same error as below?
To further investigate the issue, I’d like to confirm the following information:
- Go to http://teams.microsoft.com/downloads and download the desktop client. After that, log into the client to check if it works.
- About those one who cannot login Teams, do they use the same browsers as others? Please share what browsers they are using and the versions of browsers with us. (Note: Microsoft Teams supports the web client on Microsoft Edge 12+, IE 11+, Firefox 47.0+ and Chrome 51.0+.)
- Let those problematic users switch one of the PCs of some users who can login successfully to do the sign-in, is there any improvement?
More information in Introducing Microsoft Teams—the chat-based workspace in Office 365.
Thanks,
Lance