I have just encountered this issue. I can see in SvgHandler.php that you are attempting to Fallback because symlink often fails on Windows from a symlink() call to a copy() call, but this does not seem to be working. I think the symlink() call throws an exception in this case (not even sure PHP has exceptions), whereas your code is testing the return value of symlink(). According to the documentation for symlink() it sounds like it returns an error value in cases where the link already exists or the target does not exist. It (I guess) does not return an error value but throws an exception on permission denied. For me, when this happens, I get a 500 error from a normal PC, and the following error from the server: