CreateParameter - Stored Procs on SQL7

[Toot]

Hi all. I'm trying to append a varchar parameter like this:

Dim cm As New ADODB.Command

With cm
     .ActiveConnection = cn_INOUT
     .CommandType = adCmdStoredProc
     .CommandText = "AddAttribute"
     .Parameters.Append .CreateParameter("FormatID", adInteger, adParamInput, 4, iFormatID_IN)
     .Parameters.Append .CreateParameter("AttributeName", adVarChar, adParamInput, Len(sAttributeName_IN), sAttributeName_IN)
     .Parameters.Append .CreateParameter("Data", adVarChar, adParamInput, Len(sData_IN), sData_IN)
     .Execute
End With

Set cm = Nothing

But I'm running into a bit of a problem when sData_IN is a zero-length string - VB errors with "The application has improperly defined a Parameter object."

It works when sData_IN is anything over zero-length so I assume I've somehow got to tell it that ... but how? My field definition allows nulls.

TIA if u can help!

Toot