I just tried placing the same order to see if it would work with the code change and it has made no difference :O(

any suggestions what I can do?

here is the debug code of the retry:
| mc_currency = GBP
| submitted_currency = GBP
| order_currency = GBP
| mc_gross = 36.37
| converted_amount = 36.36
| order_amount = 36.3632

Dec 05 2012 19:51 -- IPN NOTICE :: Failed because of currency mismatch.