Proxy Error on individual pages but not on homepage?

Hey there, just a quick question, iv contacted my server but they say everything is ok on their side. Basically my website is running incredibly slow, if you go through the home address it works, but if you click through on individual pages 9/10 its not loading up or coming up with these errors:

Proxy Error

The proxy server received an invalid response from an upstream server.
The proxy server could not handle the request GET /2010/10/14/top-gun-2-in-the-works-paramount-want-jerry-bruckheimer-tony-scott-tom-cruise-back-on-board/4122/.

Reason: Error reading from remote server

or

HTTP – 500 Internal Server Error
The page you are attempting to load returned an error.

or

HTTP – 502 Bad Gateway
The page you are attempting to load returned an error.

any idea how i can fix this issue, or what i should be looking at?