"Cannot load type library for ..."

I have various VB.NET projects that include a reference to a COM object
called CMI.DLL. This COM object is something I've created myself in VB6 as
an ActiveX DLL project. Everything works fine in all projects ... I can
access CMI.DLL by making calls to it, and it returns the desired data to me
in response to my calls from VB.NET.

However, every once in a while (ie: once a week) VB.NET gives me messages
saying that the type library can't be loaded for CMI.DLL. To solve the
problem I've found that I can go to a DOS prompt and type "regsvr32
cmi.dll". This seems to fix it, because then VB.NET is satisfied when I add
the COM reference to CMI.DLL.

Given that I've made no changes to CMI.DLL (therefore it's GUID should not
have changed) I should not have to re-add the reference to it into my VB.NET
project.

What could be the problem here? I have a band-age solution, but prefer to
have things working properly.

Thanks in advance,

Tom