"Invalid Descriptor Index" while setting rdo parameter direction

[Rick]

I was working on a large, legacy VB6 program when some code that hasn't been
touched for years began failing consistently on one and only one (client)
computer. No such problem on any other developers' machines.

I think some dll file or something has become corrupted. but I have loaded
all oustanding SQL Server 2008 hot fixes and have uninstalled and
re-installed VB6 - but no change. I find it hard to believe that rdo
communicates with the server when setting up a stored procedure parameter,
but the error message indicates that it's a sql server driver issue. Maybe
it validates parameter info as it is set?

- error message: "51002: [Microsoft][ODBC SQL Server Driver]Invalid
Descriptor Index"
- program lang: VB6 (SP6)
- client OS: XP
- technology: rdo
- database: SQL Server 2005 on server; using SQL Server 2008 client tools
- code:

Set m_q = New rdoQuery
Set m_q.ActiveConnection = DB.Connection
m_q.QueryTimeout = 0
m_q.SQL = "execute member_find ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?"
m_qFindResults.SetParam 0, rdParamInput, True

[ more statements defining other parameters ]

Sub SetParam(ID As Variant, Class As RDO.DirectionConstants, Optional Value
As Variant)
m_q(ID).Direction = Class <--------- error raised on this line
If Not IsMissing(Value) Then
m_q(ID) = Value
End If
End Sub

Note: parameter constant rdParamInput resolves to 0