Cannot upload Watermark - NOT a file issue

Not sure what is happening here, but i've tried to upload a watermark using firefox, Internet Explorer, and chrome, all of which show the same problem.

The issue is, when i go to Admin > Content > Watermarks => and click the " Upload Watermark " button. all i get is a blank box.

Image:

[IMG]http://i.imgur.com/Cb4MCuy.png[/IMG]