Internal Server error

I am randomly getting these 500 errors when viewing my site pages. Not sure if it's due to the W3 Total Cache plugin I installed. I use Woprdpress v 3.0.3

Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator, webmaster@my and inform them of the time the error occurred, and anything you might have done that may have caused the error.
More information about this error may be available in the server error log.
Additionally, a 500 Internal Server Error error was encountered while trying to use an ErrorDocument to handle the request.

Error log attached