Unable to answer Facetime after upgrading to Mavericks

This is a very weird problem but this has happened both on my macbook pro and my imac. After upgrading to Mavericks, basially I am unable to answer facetime when being called. It means that the green light next to the camera turns on and the computer starts ringing but neither does it show any option for answering the call nor does the facetime show up on desktop. Am I the only have having this issue??