Looking around at various findings at other sites, this seems to be related
to either many forms (perhaps redundant) or having lots of macros causes this
problem for some people.  It can also appear when running some other
applications.

Some other links discussing the problem:
http://www.ureader.com/message/1346459.aspx
http://www.excelbanter.com/q-t_37559-FilePath-Error-then-&H8000FFFF.html
http://www.mrexcel.com/archive2/46200/53651.htm

You said you are using Office 2003, was the file created with Excel 2003 or
an earlier version?  How much memory does your computer have?