Problems with Synchronization , ERROR: invalid base64 string for MIME - Content

we`re using an exchange server (SBS), every time EM starts a Synchronization we have this ERROR: invalid base64 string for MIME - Content. no idea whats wrong!

Would be nice to get help 


Hello Oliver,
could you please copy the full content of the Log tab (from the same Operations window) when the Error message pops up again?