Vb6 and Msaccess2003 handel Null

Environement - Vb6 +MsAccess2003

Dear
I am trying to run this query in Vb6
select sum(Nz(loanamt)) - sum(Nz(retamt)) - sum(Nz(deposite)) as bal from tr_table where accno=12 and loan_type='Type2'

but vb is givng error as it doesnot identify Nz.

Pl. give me a solution which suits here.

Is urgent

Thanks
Neeraj