CGI.pm will look among the following directories for one that is writeable to your CGI user (non-Unix directories left out):

Contents of environment variable TMPDIR
/usr/tmp
/var/tmp
/tmp
/temp
current working directory
[download]

In your case, none of the above directories seem to be writable to your CGI user.

The easiest solution is probably to set $ENV{'TMPDIR'} in your code to point to a directory that is writable to your CGI user.

CU
Robartes-