Facetime constantly says "FaceTime Failed" after a call is either answered by the other party, or an incoming call is answered on the computer. Using another Mac in the same house that works fine. iMac OS X 10.7.5 fully updated.
The following article details a number of steps that can be useful in getting FaceTime working on the affected Mac.
FaceTime for Mac: Troubleshooting FaceTime
Retrieving data ...