[pmwiki-users] no file uploaded

[sim at abstr.us]

Hello List

I have a problem uploading files..

i have
file_uploads = On
upload_max_filesize = 32M

in my php.ini

and i have
$DefaultPasswords['upload'] = '';
$EnableUpload = 1;
$EnableDirectDownload = 0;
$EnableUploadVersions=1;
$UploadMaxSize = 1024 * 1024 * 10;

in my config.php

but if i want to upload a file (.png) into my pmwiki 2.1.27, the message
"no file uploaded" appears.

does anybody know what this could be?
what else should i check?

Thanks in advance, Simon