exeSortSearchListQuery SELECT command

[facciadaweb]

Hi everyone!

Straight to the problem: I get this message error -> vmError: exeSortSearchListQuery SELECT command denied to user 'myusername'@'myhost' for column 'virtuemart_product_id' in table 'l' SQL=SELECT SQL_CALC_FOUND_ROWS * FROM `italiacom_virtuemart_products_it_it` as l JOIN `italiacom_virtuemart_products` AS p using (`virtuemart_product_id`)group by p.`virtuemart_product_id` ORDER BY product_sku DESC LIMIT 0, 10
Not only for products but even for paymentmethods and shipmentmethods.
If I want to create a new product, I can but I can't see it in the backend. If I go to PhpMyadmin I can see the tables and I can make some query with no problem too.
I get the same errors if I try to make a menu linked to the products.
I should update often the products and the only way is doing via PhpMyadmin at the moment.
Any suggestions or solutions?
Thanks in advance. 

EDIT: My configuration is Joomla! 2.5.6 - VirtueMart 2.0.8