Thread:Extension talk:MsUpload/Bad RequestBad Requestunknown function SpecialUpload::ajaxGetExistsWarning/reply (2)

It works for me with 1.23.3. Have you tried the new version 9.5.1? Download from the authors site: http://www.ratin.de/msupload.html Sadly no one maintains the GIT repository. The author only maintains the "external download".

Don't forget the LocalSettings.php entries as written in the new README file.