Invitation processing seems to hang

Hi List,

I cannot seem to accept invitations any longer.  When I click the email 
I see the invitation header in yellow with the spinning arrows and 
"Loading" but that never resolves into the action buttons.  It does not 
seem to matter what the source of the invite is, I have tried invites 
from Kolab, Google, and Exchange.  I started seeing this behaviour 
around June this year but it wasn't too frequent and didn't have a 
pattern.  At this point I cannot accept invitations for days at a time 
and then it will "magically" work again for some time.  I don't see any 
indication of what is failing or timing out in my logs and restarting 
services or the machine does not help.  What should I be looking for and 
has anyone else seen this?

Thanks,
Eric