Help with Error "MIsmatch in expression"

[RXLPA3]

I am getting the following error "mismatch in expression" when trying
to run my update query,

UPDATE tblCardinalPurchases INNER JOIN tblKrogerStores ON
(tblCardinalPurchases.CUSTNAME = tblKrogerStores.CUSTNAME) AND
(tblCardinalPurchases.CUST = tblKrogerStores.CUST) SET
tblCardinalPurchases.STORE = [tblKrogerStores]![Store];

If you need additional information let me know, as I have only been
working with access for 2 weeks.

Thank You!