Hello all,
I was struggling with the same problem - blank page after confirmation of COD (cache on delivery) payment and I have found the solution:
edit the file /config/config.inc.php
and insert this line:
ini_set('display_errors', 'on');
this will show the error instead the blank page - in my case it was insufficient memory, which can be fixed with inserting this line: ini_set("memory_limit","128M");
Hope this will help other users in the future