debug issue: aspnet_wp.exe drops from debugged processes

[NancyASAP]

Using VS 2003 .NET 1.1. Debugging works fine except under one
condition.

In my code, I instantiate an object that references a vendor .NET
assembly wrapping a COM object. Debugging works up to the point in code
where I execute a method on that object (myObj.StartPrinting).

After line executing the method, all debug breakpoints cease to
function. Opening Debug Processes window, I see that the aspnet_wp.exe
process is no longer listed as a debugged process.

The only thing that I have found that allows debugging to work
correctly after this is to exit out of Visual Studio and restart the
project. Debugging attaches again to aspnet_wp.exe correctly.

More info:
- Not debugging remotely. - .NET assembly and COM object it wraps are
local on my PC.
- As long as I never step into the line of code calling the method on
the object, debugging works fine and aspnet_wp.exe remains listed as a
debugged process.

Can anyone tell me what might cause the debugging to not work only
after calling into this object?

Thanks
nancyasap