Items per page on virtuemart category 404 error

[nickel21]

I have installed  sh404 and that need to have a itemid in no sef url in order to product the sef url
in the pagination of virtuemart missing itemid VALUE and for that reason it is not possible to product the right not sef url and as result to have 404 no found page
a example is the following
index.php?option=com_virtuemart&Itemid=&keyword=&limit=15&view=category&virtuemart_category_id=71&lang=el
and should be like index.php?option=com_virtuemart&Itemid=9999&keyword=&limit=15&view=category&virtuemart_category_id=71&lang=el
what should check or change in my site .

thanks