c# updating table using LINQ to SQL?

c# updating table using LINQ to SQL?

I'm trying to update my table with this LINQ query
public void updateProduct(
int selectedIDToUpdate,
string prodNAMEToUp,
double prodPriceToUp,
string prodTYPEToUp,
int prodMANUToUp,
int prodCODEToUp)
{
DataClassesLINQEPOSDataContext dcld = new
DataClassesLINQEPOSDataContext();
TBLPRODUCT tblprod = (from prod in dcld.TBLPRODUCTs
where prod.product_id == selectedIDToUpdate
select prod).First();
tblprod.product_name = prodNAMEToUp;
tblprod.product_price = prodPriceToUp;
tblprod.product_type = prodTYPEToUp;
tblprod.product_manufacturer = prodMANUToUp;
tblprod.product_code = prodCODEToUp;
dcld.SubmitChanges();
}
and then when I start to run the program I have this error
"InvalidCastException was unhandled" "Specified cast is not valid."
Sorry I cant post image because I dont have enough reputation "points" :(