samba - Dec 2005 - Cannot exec program from network drive after 10 minutes

Hi list,

following (very strange) problem:
An ordinary windows user has mapped a drive F: on \\LUN1\Programme 
(running samba-3.0.20b-3 debian). The program "F:\Network\PMail 
V3\Pegasus Mail\winpm-32.exe" is being started, this works.
But after about 10 minutes, the same program start fails with "invalid 
path or filename".

When accessing the F: drive via Windows-Explorer, the drive is being 
reconnected and the call of the winpm-32.exe is successful again.

What the heck could be wrong here?

I have attached loglevel-10 logfiles and my smb.conf as .tar.gz.

Please help, I've got stuck in deep mud here.

Many thanks & regards,

-Andreas.