Cannot uninstall deployment

[Alistair]

One of my clients recently successfully installed a web application
from a WebSetup.msi file created in visual studio. They have
uninstalled and upgraded a couple of times since then with a new
WebSetup.msi file. (during initial test review phase)
For some reason - all of a sudden they can't uninstall the existing
web application via programs install/uninstall. It came up with the
error.

"The installer has insufficient privileges to modify this file:
c:\Config.Msi\xxxx.rbf (where xxxx I imagine is a unique number)"

I read somewhere that this may have been due to the client running
some kind of spyware removal tool that removed the Config.Msi folder,
and to remedy this just create the folder again and it should resolve
the problem.

I tried this and now when the client tries to uninstall the web
application it comes up with a different error.

"The installer has encounterd an unexpected error installing this
package. This may indicate a problem with this package. The error
code is 2203."

I would be grateful for any help, in the first place with an
explanation of how to simply remove this from the clients program list
(the easist way possible), and secondly to help understand whats going
on to address this problem should it occur in the future.

Many Thanks,

Alistair