Thanks - after turning error reporting on I get the following errors:
Warning: session_start() [function.session-start]: Cannot send session cookie - headers already sent in /WA_ValidationToolkit/WAVT_ValidatedForm_PHP.php on line 3
Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at /WA_ValidationToolkit/WAVT_ValidatedForm_PHP.php:3) in /WA_ValidationToolkit/WAVT_ValidatedForm_PHP.php on line 3