During the migration process from Vista to Windows 7, some of the settings for Communicator can get corrupted. This does not happen for new installations of Windows 7, but only situations where user state is migrated. Screen pop-ups for incoming calls do not appear. Uninstalling and Reinstalling Communicator does not fix the problem – additional registry keys and file paths need to be removed. The work-around is to:
1. Exit Outlook & Communicator.
2. Uninstall Communicator, Live Meeting and Live Meeting Conferencing Add-In for Outlook
3. Delete HKCU\Software\Microsoft\UCCPlatform\Communicator And HKCU\Software\Microsoft\Communicator
4. Delete C:\Users\(username)\AppData\Roaming\Microsoft\Communicator
5. Delete C:\Program Files (x86)\Microsoft Office Communicator (for 32-bit operating systems, the x86 will not be there)
6. Reboot, and then install Communicator R2.
Additionally, some users have reported that they no longer hear communicator ring when an incoming call comes in. The fix for this is to change the sound theme back to Windows Default.
Lastly, in the event that all else fails, the last resort is to logon as local admin to the machine, rename the user profile, and that will definitely fix the problem, allowing screen pop-ups to show for incoming calls.