ODBC driver breaks using LOBs or long VARCHARS

Has anyone seen this problem?

We have a VB application that communicates with the database using ADO
and ODBC.  Original development was done against MS SQL Server, but we
have recently implemented it against DB2/400, and it worked fine.  On
one file there is a long field which was defined as a VARCHAR(2000).
Requirements changed, and it will now have to hold considerably more
data (an XML message, not that that makes any difference).

Initially we set it to a VARCHAR(10000).  This works fine on SQL Server,
but does not against DB2/400.  We have tried various lengths of VARCHARs
and CLOBs.  For either data type there seems to be a length above which
the data is not returned correctly.  Unfortunately, this is the hardest
type of problem to diagnose, as it is intermittent.

There appear to be two distinct classes of error: if we use a CLOB with
the default size (which I believe is 1MB), the application gets null
returned for that field, despite the fact that there is data in it
(indeed, it is defined as NOT NULL).  If we use a shorter CLOB or
VARCHAR, the application will successfully read several records, then at
some arbitrary time it will fail; the debugger shows an error in a
Microsoft DLL: this has been MSADO15.DLL and MSDART.DLL.

We have opened a PMR with IBM, and they are looking into it, but any
supporting information from you guys would be helpful, as would any
solutions or workarounds you might have seen.

The AS/400 is at V5R1, and Client Access Express is at the service pack
that came out on the 15th of February.

I am waiting for a license code from HiT Software, to try an evaluation
copy of their driver, but we would prefer to stick with the IBM one
rather than pay for an alternative.

Cheers,

Martin.

--
Martin McCallion
Senior Technical Consultant
Work:  martin.mccallion@misys.com
Home: martin.mccallion@ukonline.co.uk
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