I am sure this kinf of update query does not work in VFP 6. If you switch to VFP 9 then you may use following syntax:
Update EMP SET EMP.card_id = ACCT.card_acces ;
from ACCT ;
WHERE upper(ACCT.last) = upper(EMP.last_name) ;
AND upper(ACCT.first)= upper(EMP.first_name)