Thanks - the logs appear to be in mydomain.com.au/zencart/logs. The latest entry says:

Code:
[25-Jun-2014 18:25:58] PHP Warning:  Unexpected character in input:  '\' (ASCII=92) state=1 in /home3/aap/public_html/zencart/includes/modules/payment/eway_rapid.php on line 131
[25-Jun-2014 18:25:58] PHP Parse error:  syntax error, unexpected T_STRING in /home3/aap/public_html/zencart/includes/modules/payment/eway_rapid.php on line 131