Here are a few troubleshooting steps you can try to fix the problem:
- Clear Skype for Business cache: Close Skype for Business and navigate to the following folder: %userprofile%\AppData\Local\Microsoft\Office\16.0\Lync. Delete all the files and folders within this folder. Then, restart Skype for Business and check if the issue is resolved.
- Repair Office installation: Go to Control Panel > Programs > Programs and Features. Find Microsoft Office 365 in the list, right-click on it, and select "Change" or "Repair". Follow the prompts to repair the Office installation. After the repair process is complete, restart your computer and check if Skype for Business is working correctly.