problem with samba

[Luca Ferrari]

Hi all,
I've got a ubuntu 6.1 server running samba and I'm experiencing a problem 
running samba.  I've got a list of 
users allowed to access a disk share from their windows machines, and the 
clients save files (such as .doc and .xls) in the share. Sometimes certain 
files disappear, that is the client is no more able to see them. I've tried 
changing permissions, ownership, name and position (i.e., moving them to a 
different share) but nothing worked. The only thing I found to solve the 
problem is to zip all the share content and then to unzip it from a windows 
machine, then all the clients see again the disappeared file.
I've tried to check the unzipped file with the original one but the checksum 
is the same and diff does not report any difference. Moreover, from the dos 
command line the file is visible and if you spoecify the file name in the 
explorer path you can open it. So the file is there, can be accessed but 
simply is not shown. The name of the file has no strange characters and 
permissions are ok.
Any idea about what can cause this behaviour and which configuration option to 
work on?

Thanks,
Luca