My other user acconts which are not administrators but can only upload and delte (modify) their files are not able to upload using the upload tool. I get an error message saying "File upload failed"
I guess the user under which the webserver process runs (maybe apache) does not have write access to the directory you want to upload files to. Ensure that the webserver process has write access to the upload directory:
(1) Find out under which user the web server process runs on your system (on unix systems try "ps aux | grep httpd"). The first column should show you the user name.
(2) Give this user the ownership of the upload directory ("chown <username> myuploaddir")
Are you sure that the admin user may upload files? I guess, he also cannot upload files except he uploads file to other directories.
Also check your php.ini for file_uploads (should be turned "On").
Which version of quixplorer do you use?