Temporary (volatile) Jet DSN For Process 0x508 Thread 0x634 DBC 0x2181024 Jet

I am using ASP + IIS + MS access, when running the following codes:

set Conn=Server.CREATEOBJECT("ADODB.CONNECTION")
conn.open "DRIVER={Microsoft Access Driver
(*.mdb)}; " & Server.MapPath("db.mdb")

The following erorr is show:

General error Unable to open registry key
'Temporary (volatile) Jet DSN for process 0x508 Thread 0x634 DBC 0x2181024 Jet'.

I have shared the MS knowledge base and try to grant the modify Permissions to IUSR_SERVER on the folder that holding the database, and set the script authority in IIS, the error is still exist. If I create a system DNS for that Access file and modify the second code as ...

conn.Open "AKmobile"

Another error is show:

[Microsoft][ODBC Microsoft Access Driver] The Microsoft Jet database engine cannot open the file '(unknown)'. It is already opened exclusively by another user, or you need permission to view its data.

But there is no problem when conencting with MS SQL Server.