Image upload: File is uploaded, but further nothing happens

I recently upgraded to version 2.6, and i can't get the image upload working. I am using php, so i am sure the two variables in fckconfig.js are configured properly:
var _FileBrowserLanguage = 'php'
var _QuickUploadLanguage = 'php'

In /editor/filemanager/connectors/php/config.php I have set enabled to true:

$Config['Enabled'] = true ;

These are the only things i have changed, the folder /userfiles was already present.

When i test the upload with /editor/filemanager/connectors/uploadtest.html, the file gets uploaded and i get a confirmation.
BUT! When i use the upload-function in the image-window in the real editor, the file gets uploaded, but after that i don't get any confirmation! Neither does the URL gets filled in on the first tab.

I have no idea what i am doing wrong. The test-function works, the file gets uploaded, but the last, important step is not executed.
I have tried IE and FF, both with no differences.
Please help me...

PS In version 2.4.3 everything is working fine.