unable to use upload

hi,

I am using the Drupal wrapped version of Ckeditor, and I used the files drom CkEdit ckeditor_4.0.1_standard to finish te installation.
All files have been adjusted according to the install readme specifications.
The CkEditor works just fine and I am able to add funcitonality as needed.

But there an issue with tryong to use image uploads.
I already tried using the ImageUload plugin and also the CKFinder to be able to get my pictures uploaded.
In both cases however, I'm able to install full functionality (I see the icons appearing in the CKEditor and I can use them) but no pictures will upload).
You can see the attached screenshot.
When you select a file (which works) and click "send to server) the progress bar goes half way and then nothing more happens.
This is the case with both methods.
The rights management of the destination folder (\drupal\sites\default\files is set to 777 so it can't be an issue with rights there.

Could anyone advise me where to look? I can't seem to get this to work...

thanks!