Thread:Project:Support desk/Can't upload mwstore://local-backend/local-public/reply (4)

I hope you've found the solution already, but if not, this is maybe a solution for you. I had the same error message, and all I had to do is to run chmod -R 777 ./images inside my mediawiki root directory (this is the default upload directory, if yours are different, then of course you have to do it for your upload directory), since it was a permission problem. Since then, the file upload and the math expression generation (this is where I first found error) works perfectly.