[MarketPress eCommerce] Marketpress variations

Hi,
I have an issue with
http://fastformations.webediser.fr/produits/
when I choose a variation : failed to load mp_product_attributes because the link is bad (not relative) http://wp-admin/admin-ajax.php?action=mp_product_update_attributes
Other websites on the network with domain mapped don't have this issue.
Could you fix this ?
Support access granted.
Best regards
Frederique