MDAC error opening Access DB under ASP.NET

[Guest]

The following error occurs trying to open my Access database with ASP.NET app:

The .Net Data OLE DB Provider(System.Data.OleDb) requires Microsoft Data
Access Components(MDAC). Please install Microsoft Data Access
Components(MDAC) version 2.6 or later.

System is XP SP2. MDAC is 2.81. JET is latest SP. .NET is 1.1. MDAC
reinstall doesn't help.

This is using impersonation to open the user's database. The same code and
connection string to open the database works fine from a .NET desktop
application. So, what gives?