Update/upload problem Error 500

I have tried downloading and uploading the new theme folder multiple times. Every time I use the new updated folder and web link just brings up Error 500. I have kept a backup of the old folder as suggested in the How to update thread so renaming it restores the old version fine. I can’t work out why the new version won’t load. Activating the new theme within the theme manager also makes all links “Error 500”

I’ll keep trying but i’m not sure whats causing the problem at the moment.