Master-Details Insert

Master table (tlbProduct) having productID as Primary key and
which acts as reference key for table (tlbCategory).
Fields for tlbProduct are productID,productName
Fields for tlbCategort are productID,CategoryID(primary key),CategoryName,Prize
both productID,CategoryID are autoincrementing.
but when i write two inserts simultaneously as follows
insert into tlbProduct(productName)values(@productName)
insert into tlbCategory(CategoryName,Prize) using sqldatasource
I get the error that ProductID value is null which is not provided
But (productId in both is autoincremented) and relationship is there in both tables
How to resolve this problem without adding ProductID in second Insert
?
SWati