No files showns in file_field

I am using IMCE for a file field as administrator. To open IMCE, I click on "file browser" in my content element field. IMCE is shown, but no files are shown. Only the folders in /sites/default/files... but every folder seems to be empty. I checked it in the filesystem: None of these folders is empty.
When I click on my user page, I can open IMCE as well. There are more Buttons like "delete, upload, thumbnails, resize" which aren't displayed in the other case.

Is it a bug or did I made a mistake?

Thx