Double SQL Join Problem Through ODBC

I have experienced problems issuing SQL containing multiple joins through an ODBC connection. I read a thread here, which suggested an alternative to using multiple joins, this I tried and it appears to work. The code is as follows:

SELECT tblCust.AccountNo, tblCust.SalesMan, tblCust.AccManager, MAX(CASE WHEN SalesRep.Rowid = tblCust.SalesMan THEN SalesRep.Name END) AS SalesManNa, MAX(CASE WHEN SalesRep.Rowid = tblCust.AccManager THEN SalesRep.Name END) AS AccManNa
FROM Customers tblCust INNER JOIN SalesRep ON tblCust.SalesMan = SalesRep.Rowid OR tblCust.AccManager = SalesRep.Rowid
WHERE (RowID = '1126318')
GROUP BY tblCust.AccountNo, tblCust.SalesMan, tblCust.AccManager

However, I would like to know how efficient such code is compared to my original (and problematic) joining.

The following is a summary of my original problem

I have one view (Customers) and a table (SalesRep). Customers contains a list of customer companies, while SalesRep lists internal staff. Each company record has fields to identify a Sales contact and an Account Manager, both of which would be listed within the SalesRep table and could be the same person.

It seems fairly straightforward, we are using two INNER JOIN's between the tables, as follows simplified query shows:

SELECT tblCust.AccountNo, tblCust.SalesMan, tblCust.AccManager, salesRepTbl1.Name AS SalesManNa, salesRepTbl2.Name AS AccManNa
FROM Customers tblCust
INNER JOIN SalesRep salesRepTbl1 ON tblCust.SalesMan = salesRepTbl1.Rowid
INNER JOIN SalesRep salesRepTbl2 ON tblCust.AccManager = salesRepTbl2.Rowid
WHERE (tblCust.Rowid = '1126318')

This works fine when executed on SQL Server, as following result:

AccountNo---SalesMan---AccManager---SalesManNa---AccManNa
1234567---100---106---John Smith---Carol Flood

However, when issued using ASP through an ODBC connection to an Intersystems Cache database - SalesManNa is showing the result expected for AccManNa, as...

AccountNo---SalesMan---AccManager---SalesManNa---AccManNa
1234567---100---106---Carol Flood---Carol Flood

Interestingly, the above query does not return any results when executed through Vis Web Dev 2005 Express.

We are using a DSN for the connection, which uses the InterSystems Cache ODBC driver (5.2.0.329.0). I have tried many variations on the join and different syntax but no success and I'm not privy to any specific ODBC restrictions.

Any pointers as to what may be causing the problem through ODBC would be greatly appreciated as would any opinion of the efficiency of the working solution.

Many thanks,
Cliff