First thing to check: Slasharguments
If you have moodle 1.7 try Administration -> Server -> HTTP and change Use slash arguments setting. If you have moodle 1.6 go to Administration -> Configuration -> Variables and find slasharguments: change it to other value. Save changes.
If this does not help, next question is: where and how did you upload that file and did you get the link clicking the file or writing some address?