Update fails when carried out from non-admin account

[chrizio]

Frequently in short time period lot of XnView updates are released/issued.
Therefore the update procedure must take no more than few minutes.

However, it does not succeed if to carry it out in following way.
Windows XP SP3, ShellExtensions for XnView are installed and enabled.
User logged to its own Windows account where normally he/she is
doing own regular/all-day jobs, an account without administrative privileges.
User starts XnView for short time using "Run as..." -> administrative account,
just to switch off ShellExtensions. After that it starts the installer of XnView newest version,
again using "Run as..." -> administrative account.
The update/installation procedure stops on stage where some ShellExtensions dlls/files
are to be copied from installer package to disk. The quick and cheap update is no more possible.
User has to restart the PC, to log-in as administrator and repeat the update procedure
in order it completes successful.

Yet worser it is on Vista (possibly also Win 7) systems where UAC is enabled.