Upload not possible on subdomain
 

I recently installed a 0.11 version of phpwebsite on a subdomain of one of my domains. Just for testing. And now I found out that I cant upload files with the Uplink module or the Documents module. They both seem to upload the file without errors. But the Documents module doesnt display the file. The Uplink does show the link to the file but the link is not working. And in both cases the file is not in the directory where it should be.
No messages in the error log.
Anybody?