Facetime with iPad won't work after 6.1 Update

Is anyone having issues making calls to iPads from iMac (OSX 10.7.5 Lion) after the iPad has upgraded to iOS 6.1? It worked before I updated the iPad, and it still works with my iPhone after upgrading that to iOS 6.1. I have tried with other non-upgraded iPads and it works, but other upgraded iPads do not work as well.