Correct programming errors on my premiumpress-wordpress website

I have 5 websites which use shopperpress 6.2.2

They are pretty heavily customised through my programming as well as programming from other sources. I have a couple of issues and would like some changes made for which need a shopperpress expert.

I believe some customers can not properly checkout due to a validation on the checkout page.

I have received several emails from people across my 5 sites saying that the 'checkout' button is not clickable for them even though it should be. I have also had customers saying it will not proceed as there email addresses are judged not to be valid even though they are. When I have tried to recreate the problem i can't even on different browsers, computers etc

So basically I have some checkout problems which need resolved.