Image Upload works, but "Browse Server" > Upload doesn't

I'm able to upload images if I open the "Image Properties" window, click on the "Upload" tab, and follow the steps from there. However, if I click on the "Browse Server" button in the "Image Properties" window, and try to upload through the Resources Browser, images are not uploaded. I browse, select a file, and hit upload. The "Image is being uploaded.. please wait" message is displayed, but then simply disappears and nothing else happens. The image is not uploaded. I cannot create folders either. When I try, I get "Unknown error creating folder." Anyone have any idea?

Thanks!
tjk