DTS Type Mismatch at Join

I am new to ETL and VB in general and need some help resolving this issue. I have looked online and found some interesting answers but none seem to be working for me. varamt = Lookup ( "Lookup_tbl1", [Lookup_tbl1].[Amount], Array(DTSSource("DEPT_ID"), DTSSource("ACCT_ID"))) IF NOT isEmpty(varamt) or NOT isNULL(varamt) or NOT varamt="" THEN DTSDestination("AMOUNT") = varamt ELSE DTSDestination("AMOUNT") = DTSSource("AMOUNT") END IF Lookup_tbl1 has ACCT_ID and DEPT_ID as the primary keys. My destination table does not have these as primary key and ACCT_ID has NULL values in the table. Dept_ID and Acct_ID are varchar. When I tried this transformation where ACCT_ID was not NULL, it worked, but not in the table where I want it to work. Here is the error message that I get: Inserting into [AMOUNT] ... Error details: The number of failing rows exceeds the maximum specified. (Microsoft Data Transformation Services (DTS) Data Pump (80020101): Error Code: 0 Error Source= Microsoft VBScript runtime error Error Description: Type mismatch: 'Join' Error on Line 36) Execution Failed.` There is no line 36 in my code. Please suggest solutions / pointers.