This error, has been bugging me for a long time.
In the past I managed to solve it by applying the instructions on this kb: http://support.microsoft.com/kb/896861
However I felt it was not "fully supported" for OCS. Well I was mistake, since recently I spotted this other article: http://technet.microsoft.com/en-us/library/bb663688.aspx, but exactly for OCS!
Well, I'm happy!