Problem with .NET application accessing MS Exchange Server 6.0

[Arun T M]

I have a Windows Service written in VB .NET which
connects to an Exchange Server and accesses the messages
in the Public Folders. I am using Collaborative Data
Objects to do this. When I run the service, I get the
following error...

System.Runtime.InteropServices.COMException (0x80010106):
[Collaboration Data Objects - [UNKNOWN_ERROR(80010106)]]
at System.RuntimeType.ForwardCallToInvokeMember(Strin g
memberName, BindingFlags flags, Object target, Int32[]
aWrapperTypes, MessageData& msgData)
at MAPI.SessionClass.Logon(Object ProfileName, Object
ProfilePassword, Object ShowDialog, Object NewSession,
Object ParentWindow, Object NoMail, Object ProfileInfo)
at EMailParser.EMailParser.EmailApp()

My logon method looks like this ...

oSession = New MAPI.Session

'** Logon to the Exchange Server **'
Try
oSession.Logon(, , , , , , server & vbLf & user)
Catch e As System.Runtime.InteropServices.COMException
EventLog1.WriteEntry(e.ToString())
End Try

here server is the name of the Exchange Server and user
is name of the mailbox account on the exchange server.
This piece of code works perfectly on one exchange server
and does what it is supposed to do but when it is run on
another exchange server, it throws the above error. Both
the exchange servers are running Service Pack 3.

Any help will be appreciated.

Thanks in advance.

Arun