What Can Cause The Value In Application Variable To Disappear?

We have ASP application running on IIS 5.1 and Windows 2000 server. The ASP
application has few Application variables setup in global.asa. Something like
this:

Application.Lock()
Application("fun")="play"
Application.UnLock()

There is no other code in the ASP application to change the value in the
Application variables. It's only set in global.asa and the rest of the
application just read it with code similar to this:
Response.Write(Application("fun"))

The application had been running fine until we deployed a COM DLL to the web
server few weeks ago. Loos like the ASP application started to loose the
value in application variable few times a day. Restarting the web service,
which means re-initialize the value in Application object, fixes the issue
but the value will be blanked out again after few hours.

The COM DLL is written in .Net C# to handle some task. This COM has "private
static" variables in public class. The purpose for "private static" variables
is that the value will be maintained until IIS is restarted.

Is it possible that the memory space for .Net run-time conflicts with the
memory space of ASP Application object? Can someone help me understand what
can cause this to happen?