Redirect to order success page

Hi All,

burleyarms.co.nz
OC: 2.3.0.2

Have just finished updating from OC 1.5.0.3 to 2.3.0.2 and just going the process of bug fixing issues with previous modules.

I main issue i can not quite get my head around is with a Extension that is installed and supplied by a Third party credit card payment merchant and for some reason after the transaction has been processed the following error display on the front end and does not revert to the /index.php?route+checkout/success Page.

The flow2cash module creator has provided screen shots of the module functioning properly with the same version OC

Here is the front end error:
Warning: Cannot modify header information - headers already sent by (output started at /home/burleyar/public_html/catalog/controller/extension/payment/flo2cash.php:175) in /home/burleyar/public_html/system/library/response.php on line12

Can anyone shed any light on this???

Cody