WampServer

I have installed and run this TNG program (the same version even) on WAMP without problems before!
However now I have a problem.

Currently running:
WampServer Version 2.4
Apache 2.4.4
PHP 5.4.12
Win 7 64-bit+8GB memory

I get the message:

There was a problem returning data from the server. This may be temporary, so please try again later. Here is some information about the status of this request:

readyState:4
status: 500
headers: Date: Sun, 10 Nov 2013 19:36:41 GMT
Server: Apache/2.4.4 (Win64) PHP/5.4.12
X-Powered-By: PHP/5.4.12
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Pragma: no-cache
Content-Encoding: gzip
Vary: Accept-Encoding
Content-Length: 20
Connection: close
Content-Type: text/html

I have used Filezilla to ensure that I have correctly setup the 755/644 permissions. I have 20 other development websites running ok with this WAMP installation so it is not a general problem.

Has anyone seen this before? Any suggestions much appreciated!