in English because I didn't find a good solution online!
Problem: ActiveSync stopped working this weekend, and I received an error like "you don't have permissions in Exchange to sync" but that was BS. Nothing changed on my account.
We had a customer with the same problem a few weeks ago: the same no permissions error and ActiveSync stopped working. This had to do, I think, with the change of summer to winter time and an incorrect date/time setting on the Windows Mobile.
We all use client certificates, generated by our certificate authority and checking the properties of the certificate on my windows mobile showed that it was expired on Halloween! No error message indicating anything like it.
Copy and installing a new certificate on my Windows Mobile with private key didn't solve the problem immediately. I think ActiveSync still used the old certificate but deleting the old certificate and rebooting the device solved the ActiveSync problem!
I hope this is useful for some people because I was able to find the error message but not the solution!