File Upload error

I’m having trouble using the File Upload module. I think I did everything right, but during my tests I receive the following error messages:

Notice: Undefined index: userfile in /www/eh7184/public_html/tppsystem/modules/file_upload/mod.file_upload.php on line 332

Notice: Undefined index: tmp_name in /www/eh7184/public_html/tppsystem/core/core.upload.php on line 96

Then, in a grey box, is another message:

The following errors were encountered: no_file_selected

Can anyone tell me what is going on?

[Mod Edit: Moved to the Modules: Discussions and Questions forum]