Today we added a new way of uploading files to a Fatpaint project. When you open a project, you'll see an upload panel at the bottom of the page. If you use Firefox or Chrome, you'll be able to drag files to this panel, otherwise, just add files to the queue and start the upload.
Some of our users are having problems uploading files using the built-in Editor upload funcitonality which is made using Flash, so we added this new way of uploading using HTML5, hopping to solve this issue. Please let us know if this fixes the problem for you guys.