im using apache2
The php.ini files have a buffer of 4096 set which was slowing things down and causing times out but changing this didnt fix the 500 error. i followed the perfect server guide for centos 6 and ispconfig3 for info
still a little bit of a noob when it comes to finding the error logs so havent checked them, however im not over liking the centos OS so reloading with ubuntu as there seems to be much better google support
ill let you know if i still have the issue.