permissions-related question for *nix gurus

I'm trying to get something working on my server with PHP3 and am totally stumped. I've got one script that's uploading a zip file, then unzipping it's contents into a subdirectory and deleting the original file. One of the files that is extracted is another zip file, which is left intact. Another PHP script is used later to extract files from this second zip file. The owner of both of these scripts shows up as 'nobody', and the group is my common group id. When I log in through telnet (as another user in the group), I can unzip things in the second zip file. However, the second PHP script is NOT able to extract anything from the zip file. I'm working with unzip v5.40. I've tried setting permissions to 777 on the zip file, as well as the directory containing it, but that doesn't help. I've tried setting UID and GID bits on the php3 scripts themselves, but that doesn't help. The error I get back from unzip is 50, which indicates something like "disk is full". The disk is far from full. I can put a -l or -v option on the unzip command and get a listing of the contents just fine, so I know the file is readable. I put a -d option to specify the directory (the same one containing the zip file itself) so that shouldn't be a problem either. Does anybody have any idea what I can do so this php3 script can extract files from the zip file? Thanks -David