Cannot perform runtime binding on a null reference

Background:
This code is ran in a service. For every user this code is called to reset their password for this application. This is an SSO environment, but the error is reproducable outside the environment.

The error is that occasionally, I get a Cannot perform runtime binding on a null reference. I have checked that it isn't a data issue by doing this process manually. Also, I am new to this forum so if I am breaking some etiquette don't hesitate to scold me .

The code:

EXTRA.ExtraSystem system = new EXTRA.ExtraSystem();
EXTRA.ExtraSessions sessions = system.Sessions;

var session = sessions.Open("X.adp");

try
{
Thread.Sleep(2000);

*I GET THE NULL REFERENCE ERROR BELOW THIS LINE

var status = session.Screen.OIA.Xstatus;
session.Visible = true;

LOG *I GET THE NULL REFERENCE ERROR BEFORE THIS LINE

Thread.Sleep(500);

session.Screen.Sendkeys("<Clear>");

session.Screen.Sendkeys("/rcl<Enter>");
session.Screen.WaitHostQuiet(1000);
Thread.Sleep(1000);

*POPULATING SCREEN*

*Gets Screen Response and determins if successful
string screenResponse = session.Screen.GetString(23, 1, 70);

session.Screen.Sendkeys("<Clear>");
session.Screen.WaitHostQuiet(1000);

session.Screen.Sendkeys("/rcl<Enter>"); //logout|disconnect
session.Screen.WaitHostQuiet(3000);
Thread.Sleep(1000);
}
catch (Exception ex)
{
*Handle Error*
}
finally
{
session.Visible = false;

Marshal.FinalReleaseComObject(sessions);
Marshal.FinalReleaseComObject(system);
Thread.Sleep(500);
}

Technology:
C#
Attachmate EXTRA! 7.1 Object Library

My questions:
1.) Being that this happens not often, I am thinking this may due with me accessing some variable when it isn't ready yet. Does anyone see anything that may be wrong from that perspective.

2.) What is the proper way to marhsall these objects from life to death? Anything else I maybe missing here?

3.) How should I properly treat var status = session.Screen.OIA.Xstatus? I have noticed in some forum entries that this is encased in a loop waiting for the value to change to 0? Is this expected or normal behavior? I have also noticed many, maybe more so entires where this value is completely ignored.

4.) Any other tips or suggestions is helpful. Thanks


contd.

I am not sure if this is the wrong forum but if it is please let me know. If it isn't here is an update:

I built a seperate application, this time a desktop C# windows form application. I copied the code and ran it from that application and it worked. The things that are different are:
one is a service and one is a desktop app
one runs under a service user account the other runs under the user account

The desktop works but the service doesn't.

Other things to note, though these may appear to be obvious to this group, is that after running
EXTRA.ExtraSystem system = new EXTRA.ExtraSystem();
EXTRA.ExtraSessions sessions = system.Sessions;

Two processes appear and inherit the callers security credentials, ie if the windows form app is executed by me the two new processes also spawned are under my security context as well.

These are:

AccMgr32
AccSmngr

These appear to manage attachmates session and application processes for emulation and connectivity to the mainframe. One of the thoughts I am playing with is that these credentials may not have access to something required. But I have confirmed that the security credentials would not have changed recently.

It does appear that I can reproduce the same error, though may not be the error actually in question by running the desktop application under different user accounts. Ie first run it under my account and then subsequently run it under a different account and when the above two processes are running under a different account we get this error.

Thoughts?