Error when adding product to orderProduct

Dear,

On the Order page (Classic UI) with a Freedom UI environment, an user has the following message when he add a product to the order :

I can not find where the problem can come from, it happened on different computer. i tryed to remove the Creatio Cookie but the error message stil appears. When the user go back to the previous page in his navigator, the product has been add to the orderProduct.

Does anybody has allready had this problem ?

Thank you,
Nicolas