Hey Hector..
I'm sadly not a web developer so I wouldn't even have a clue where to start...
Thanks for the heads up though - I've removed a whole load of plugins today, made sure everything is up-to date, including my thesis theme.
I'll speak to my hosting company to see if I can get any help.
By the way - where do you see this 500 error? They might ask me to explain where I'm seeing the 500 error?
Thanks,