Multiple Column Join

I have two tables, one of which is a key table with a subaccount number and a set of attributes that define that subaccount. I am trying to join this key table with the table with all the attributes and come up with one table of subaccounts. The Subaccounts should only lookup the attributes associated with them, not all of the attributes, so I put OR [attribute] IS NULL in the WHERE clause so it only matched on the appropriate columns. This worked great in an initial test with two attributes but when I put all 9 attributes in it crashed with this message "Msg 415, Level 16, State 1
The current query would require an index on a work table to be built with 15 keys. The maximum allowable number of keys is 16"
like this
CREATE VIEW subaccounts
(Subacct_no, balance)
AS SELECT
(s.Account_No + "." + r.Subacct_Ext, S.Balance)
FROM Acct_Rcd r, Subacct_Key s
WHERE
(s.attr1 = r.attr1 OR s.attr1 IS NULL)
AND (s.attr2 = r.attr2 OR s.attr2 IS NULL)