Error $2B, OS Error with TUtility.DLL (rebuilding)

While trying to rebuild a corrupted paradox-table with TUTILITY.DLL on
networks, we often got the error 43, $002B, "OS Error".

After we copy the whole database local, everything works fine, but
this is very uncomfortable. I'm sure, that there is nobody connected
to the database at this situation.

Any hints?

Stefan Kirch