Outlook 2003 Add-Ins disappearing suddenly!

Hi

I am working on a VSTO Project(Outlook 2003 Add-In) which is developed
in VS2005. The problem with this is that it is working fine in some
systems. But, in some systems, the add-ins are not displayed. In some
other systems, they are disappearing suddenly, and are not installing
even on repairing or removing the old one and install again.

I have an ocx file in my project. I am getting an error while
installing - "Cannot register PluginControl.ocx". I have continued the
setup and registered that ocx file under elevated command mode. No
Luck!

The client system has Windows XP SP2 and I have installed and
rechecked the following in it.
* .NET Framework 2.0
* O2003PIA and
* VSTO Runtime - Shipped with VSTO 2005SE

I have created a new limited user account in one of the problematic
systems. The Add-In is working fine. Even-though the problematic user
account has admin privileges, it is getting error - "Not Loaded. Error
occurred while loading COM Add-In".

As this is working properly in some systems, I don't think that there
is a problem with the code.

I am fed up with this and couldn't reproduce it!
Can anyone please suggest a reason for this abnormal behavior of plug-
in? What might be wrong with that systems, specifically, user
accounts?



Thanks and Regards,
Pranav