Backup failure

[blaniosh]

I'm a new user to the application - I am VERY impressed, it is superb.
I am running the Pro version but when I press Backup from the Admin page, I get the following:

Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.

Please contact the server administrator, myemailaddress 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.

Any ideas?