can ping - but Offline Files doesn't 'see the file server'

Hi,
I am using Vista x64 SP1 (servA) as a file server and using Vista x64
SP1 also on the client side.

I earlier on was connected to a file share with \\servA.domain.local
\fileshare with credentials domain.local\user (don't know if this is
important to mention). I've made some folders to be available
offline.

If I am resuming from hibernate, I can ping my servA machine, but I am
unable to connect to my servA-fileshare. It always shows my server to
be unavailable.

If I am rebooting my client machine, I can successfully connect again
to my servA-Fileshare. I can see my online and my offline folders.

What are further steps for debugging? Are there any GPOs that could
come into play?

Thanks.
Charlie