When I try to set an Image for my collection I get this error:
"We're sorry, but something went wrong.
Please send an email to gallery@greenfoot.org for assistance.".
What am I doing wrong to get this error. On the bottom of the window (from clicking on "edit collection") is says "An image (1MB max, PNG or JPEG, will be scaled to 120x70 pixels):", but when I click on the button "Choose File" the file filter is set to .png. I could set it to All files but that's not only the extensions mentioned above (It didn't work even as a .png).

