500035 Joomla Error 500 Fix

I've just migrated a to a new server and one of my Joomla sites is giving an Error 500. I need someone to fix this. A full back-up of the site is available on my old server in case anything goes wrong. A quick, instant job would be great. I will put your fee in escrow prior to the job and release it to you once I've checked it all works fine.