Thanks for the link, I will check that out.
The Domain Controllers do nothing else then the DC tasks. The Windows version is the same then on other Windows servers. The Domain Controllers are not all in the same job. We host a lot of customers on the same platform and devided the Veeam jobs by Customer, so all of the jobs have a DC, a database server, fileserver, terminal server, etc etc. Almost all of those jobs have had the problem with the DC and not with the other servers. De C: and D: are on the same storage. The problems occurs during the first backup job (so no retry).