Try restarting your gear and check this quick workaround clears the error.
If nothing changes, follow the steps below.
Then, restart Skype, throw in in your username and password, and hit theLog inbutton.
To clear your Skype credentials, go toControl Panel, selectUser Account, and click onCredential Manager.
Then, select all theSkype entriesand hit theRemovebutton.
Check Your web connection Connection
check that there areno connection issueson your end.
Launch Command Prompt with admin rights, and run theipconfig /flushdnscommand to flush your DNS cache.
Meanwhile, power cycle your setup.
Then, plug your router back into the wall outlet, and wait until your system goes back online.
Launch Skype and test whether you’ve got the option to sign in to your account.
Repair Microsoft 365
Skype for Business is part of the Microsoft 365 suite of products.
Any issues affecting Microsoft 365 will automatically affect Skype as well.
Try repairing your Microsoft 365 installation files, and verify if you notice any improvements.
Contact Your IT Admin
If nothing works, contact your IT admin for further help.
Maybe they need to reinstall the certificate on the server where Skype for Business is installed.
Let your admin know what troubleshooting steps youve tried so far.
Then, launch the Credential Manager and delete all the Skype credentials.
Repair your Microsoft 365 installation files and contact your IT admin if the issue persists.
