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Phssthpok - IIRC there was a glitch last year with an upgrade to the msi installer that induced this sort of behaviour - it was fixed in the next set of WU patches. There's free standing fix somewhere at MS, but if your windows is up to date and you didn't discard/hide the patch you should have it.
Or something changed on your system at some stage to make the installer think you run calibre from a server. The installer uses the data from previous installs so that it can apply the same customisations. Try uninstalling calibre and then running a lightweight registry cleaner such cCleaner.
But please don't use Revo Uninstaller, given half a chance it will remove your calibre configuration data. If you haven't got a backup of it then... hint ==>>
How do I backup calibre? (
← click) - see para 3.
BR