yes that did the trick!
the code looked a little bit different at first:
/customer/main/product.tpl:
********************************************
{include file="buttons/add_to_cart.tpl" style="button" href="javascript
:if (FormValidation()) document.orderform.submit()"}
********************************************
changed to:
********************************************
{include file="buttons/add_to_cart.tpl" style="button"}
********************************************
Thanks very much netmagik! cheers!