I just tried to upload a 4.1 MB GIF to a forum post. The post editor allowed me to start the upload, and it showed the progress bar as I waited for it to finish uploading. But them, only when the upload finished, did I get this: So, two things: Don't initiate the upload that's going to fail? If you can show a progress bar displaying the upload progress so far, it means you know how big the file size is before trying to upload it. Warn users at that point that the file is too big. Tell me what the file size limit is in the error itself. Right now it just says "too large", which isn't very helpful.