smart client deployment - serious issue

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I am working on a big business application (dot-NET 1.1+legacy stuff), which
is deployed in "SmartClien t/no-touch-deployment" model. For some time on we
have a problem that nobody was able to resolve so far, although a number of
good developers have been looking at it.

Some of our users are getting an error that "resource" or "assembly" could
not be found (both exceptions are popping up - sometimes one sometimes the
other). The stack trace shows IO exception "File not found" and the path is
pointing to an assembly in "downloadab le cache". When we verify the path
that the exception is talking about, the path indeed does not exist.

The moment/place when it happens is pretty much random. For some users it
happens right at the start of the application, for some it happens after
some time of working with it. So, it looks like CLR is loosing the track of
where the assembly are physically located and is asking for something else,
or [less likely] the assembly path is deleted [but by what and how ? -
loaded assembly is locked isn't it ?]. Clearing IE cache and assembly
downloadable cache ("gacutil /cdl" command) seems to be helpful but only for
short time as the problem re-occurs sooner or later.

I was trying to learn more about how CLR is managing cache and how "Fusion"
assembly loader works but there is very little documentation.

As we are running out of time and ideas, I decided to ask on this newsgroup
for help. Not sure if this is right group though - please redirect me to
better if such exists.

Could anyone advise on how to troubleshoot/debug the problem? Where to look
or what possibly could be the reason? Any materials like web sites or PDFs
that give a clue about managing and loading assembly in Smart Client(?).

I'd greatly appreciate any form of help,

Thank you