Skype for Business, Removing stored password with Windows Credential Manager
This page describes how to clear Windows Credential Manager to remove stored Skype for Business login credentials
Windows Credential Manager is a service on Windows 7, 8, and 10 that stores login credentials to allow Skype for Business and other services to login automatically at start up. This can sometimes cause problems logging in, so one of the first steps in troubleshooting failed logins in Windows should be removing those stored credentials from the vault.
To do that you first need to make sure you have fully exited the Skype for Business client.
Then go to the start menu and find the control panel. In the control panel search for credential manager and open it up.
Under Windows Credentials > Generic Credentials there should be an entry that starts "Microsoft_OC1:uri=" and "MicrosoftOffice16_data:ADAL"
These are the stored Skype for Business credentials.
Click the downward arrow to expand the credential and then at the bottom of the credential select Remove.
Make sure to remove ALL the credentials starting "Microsoft_OC1:uri=" and "MicrosoftOffice16_data:ADAL" as any of them could be the one causing the problem.
After this try to log in to Skype for Business again.