Installation help: file uploads

Hello,

I just did a fresh install on a free provider of the latest version of
MediaWiki. Everything works, after some troubleshooting, except for the file
upload. I repeatedly get:

The file has no extension (like ".jpg").

When I try to upload a file to the site. I chmodded the images map (755),
the legal filetypes are correctly entered, I tried disabling filetype
checking all together, I tried to use another mime type detector, ., nothing
works. Can anyone put me on the right track? Before you ask, I do try to
upload a .png or .jpg file. Link to the installation:

http://bankvandetoekomst.freehostia.com/wiki

Thanks!

Joa