Unable to save files

Hi all,
I have installed the first Vista client onto my SBS2003r2 network & have
encountered an issue with saving files.
I need to point out that this user was using an XP Pro pc prior to getting
the Vista Business notebook & there were no issues. The user account is the
same & her permissions have not changed.
When creating a word (Office 2007 Pro is installed) file on the notebook,
they go to "Save as" & browse to the location on the server, via a mapped
drive, select a name for the file & click on "save" & she receives the
following error,

I:\DirName\FileName.doc cannot be found. Check your spelling, or try a
different path.
Well I have browsed to the path from within word. To check I then browse to
the location from Windows Explorer & can get there.
Can anyone help. I see that there are a few forums out there with similar
issues but no solutions.