Error pruning sharepoint versions (HTTP-status 401)

Hi,

we use sharepoint archiving.
On some files, we got the following error:

"HTTP-STATUS 401: Unauthorized. Error pruning file version"

I don´t know what this failure means. When i try to access on of the affected files directly in sharepoint with the VSA, i can open the file and all works correct.
The files are all in the same site collection and most of the sharepoint documents works fine but some didn´t work.
The VSA is  site collection administrator and local administrator on all affected sharepoint server.

This is our environment:

EV 11.0.1 CHF 3
Sharepoint 2010