I can see why you would get that result, sorry about that. The problem is that it is just telling the server go the cart page if you have Express Checkout only selected. This could be fixed by moving this code so that it is below the Express Checkout code. If you checkout page is back to the default setup then you should be able to add this code in just after the Express Checkout code that ends on line 146, it would look like this:
142: else {
143: $WA_Store_Cart->redirStr = $WA_PP_ECO_SetResult->ECOServer;
144: }
145: }
146: ?>
147: <?php if(WA_Auth_RulePasses("Using Express Checkout Only")){ // Begin Show Region
148: header("Location: cart.php");
149: }
150: ?>
Please give this a try and let us know if you have any further problems with this.