Recently I installed OA on my laptop, it worked fine until I upgraded to Avast! 6.0.1367.
No internet! 
Uninstalled OA and my internet is back! 
More bugs to fix in OA???
Not necessarily, on a program update the changed program executables will likely be blocked or at least challenged by the firewall.
First I would have checked that avastSvc.exe was allowed (not uninstalled as that doesn’t find the cause) and if so delete the entry and reconnect forcing the firewall to ask again.
DavidR,
Thanks for replying.
Actually I did what you suggested, last night, it didn’t work.
Check this link: http://support.emsisoft.com/topic/6599-oa51-issues/
I did have 5.1.