Cannot join ... are not signed by a key accpeted by this server

[Gamadeus 0]

I have Arma 2 free and OA installed with the latest patch and all together with the 1.7 DayZ mod but I still cannot join any servers.

Strangely it has something to doy with my OA files because I always get the message:...Operation Arrowhead\expansion\addons\ and then a bunch of pbo files listed that are not signed by a key accepted by this server, even though I have the latest patch 93825 installed.

I did tried reinstalling, also in different sequence but that didn´t help. Also tried everything I could find on this topic in the forum but also without success.

Anybody out there who might have a clue what´s causing this frustrating error?