The link that Ken posted suggests that it's caused by your SQL statement. Since there is only one field in your where clause, have you tried changing it to remove the ' around the AccountID? If AccountID is numeric, you shouldn't surround it with '.
Just to be crystal clear, change it to this and see what happens:
Set rsLineTotal = connection.Execute("SELECT Sum(lineItemTotal) AS sumTotal FROM SHOPPINGCART WHERE AccountID = " & Session("AccountID"))