Thread:Project:Support desk/PNG conversion failed; check for correct installation of latex and dvipng (or dvips + gs + convert)/reply

The error message is rather generic. It doesn't tell us if it failed to save the image, failed to find a executable, etc.

Enable a debug log as explained in Manual:How to debug (I think you already did that with $wgDebugLogFile ) and look for any relevant error. Since the error message may be cached, look at the debug log when previewing an edit that contains math formulas (and maybe try to change one of them), to see if it provides a more detailed error message.