What version are you running? 2.0.11 What's the URL of the page containing the problem? rb/r/new/ What steps will reproduce the problem? 1. Use Firefox 2. Select a diff file (with a "special" name, see below) to upload 3. Fill in a base directory 4. Submit What is the expected output? What do you see instead? Expected: diff file uploaded Seen: No upload and "Unknown error" message What operating system are you using? What browser? Linux / Firefox 35 Please provide any additional information below. The problem occurs on Firefox (not on Chrome). On Firefox, no HTTP request is sent (seen on Firebug network tab): the error occurs before the ajax call. The file name (in our test: "Anomalie_#331845__[inbound]_–_[TNF]_–[Return_confirmation_email]_-_Formatting.patch") seems to be the problem. After some JS debugging, I've discovered in the "_onValidateError" function that xhr.statusText="InvalidCharacterError: String contains an invalid character". I suspect one of the special characters of the file name to be the problem. The solution should be to sanitize the file name before the ajax call.