Lookup

Hi

I am using SQL2008 and am new to Report writing

I have 2 datasets:

DataSet # 1 Admissions

DateSet # 2 Referrals Placed

I am trying to create a report using  patient account # in DataSet#1 and looking up in DataSet # 2 the Name of Referral Placed Provider

I am having trouble with Lookup Syntax

=Lookup(Fields!Admission_Account_Number.Value,Fields!Account_Number.Value,Fields!Placed_Provider_Name.Value,"Placements")

Any auggestions would be greatly appreciated