Strange network problem - Can't save in Office2007 on network driv

Have a very strange problem with a new vista business computer in network
with Windows 2003 Server R2 SP2.

One of the network drive maps H: contains doc/pix/xls etc. I can access the
network drive via Explorer and copy/delete/change name of files etc from the
Vista Computer.

When I start Word2007 and load a document from the network drive it's not
possible to "save" or "save as" on the network drive. Word make filename but
it is 0kb. If I take "save as" and store the change document on Vista
Computer desktop it's no problem. And the very strange thing is that I later
can copy this file from Vista desktop into same place on network drive
without errors after closing Word. Same problem is on Excel files.

Nice if anyone have som suggestion. All Windows Updates are installed on
Vista and Office.

Thanks in advance.