Media Upload works for users with admin rights only

Hi there,

Can you please advise, how it's possible that only admin rights logged in users can upload photos?

Others get "Unable to get file list from server" error message and nothing happens if we click on Upload Media on the right top.

- we do not use Admin Tools
- group ACL has "Upload Images" rule set to "yes".
- "Maximum file upload size" is set to "2Mb".
- imasges folder permission is 755

Thanks in advance,
Zoltan