Magento Group product configrable product assign prices

Looks like you are using SCP or the SimpleConfigurable products extension. That is known to cause issues. Please try the following:

comment out lines 104-106 of /skin/frontend/base/default/js/scp_product_extension.js. However this may affect how SCP operates.
so this code:

Product.Config.prototype.updateFormProductId = function(productId){
if (!productId)
{ return false; }
var currentAction = $('product_addtocart_form').action;
newcurrentAction = currentAction.sub(/product\/\d+\//, 'product/' + productId + '/');
$('product_addtocart_form').action = newcurrentAction;
$('product_addtocart_form').product.value = productId;
};

looks like this:

Product.Config.prototype.updateFormProductId = function(productId){
if (!productId) { return false; }
var currentAction = $('product_addtocart_form').action;
//newcurrentAction = currentAction.sub(/product\/\d+\//, 'product/' + productId + '/');
//$('product_addtocart_form').action = newcurrentAction;
//$('product_addtocart_form').product.value = productId;
};