Скачал, установил, запустил. Ввел реквизиты нового пользователя --> OK -->

/********************************************************************************
QueryInterface for interface ADODB._Recordset failed.
...
System.InvalidCastException: QueryInterface for interface ADODB._Recordset failed.
at ADODB.RecordsetClass.Close()
...
********************************************************************************/


Имеем: WinXP Pro Eng, MS Jet4 SP3 OLE DB, MDAC 2.7+.

Спасибо за внимание.