My caller ID popup hardly ever works. All the calls are in the history so I know it's registering them, the popup just never comes up. I contacted tech support and the best they could tell me is that maybe it's a grounding issue and they sent me a 3-prong adapter. I installed it but it doesn't seem to make a difference.
Ditto what the others have said... Seems to happen, but noone knows why for sure. If you do get the popups, and they stop, a reboot usually seems to fix it.