We have had an unsual error when upgrading which has stalled after uninstalling and not allowing us to continue.
Installing product E:\exchangeserver.msi failed. Fatal error during installation. Error code is 1603. Last error reported by
the MSI package is 'The installer has insufficient privileges to access this directory: C:\Program Files\Microsoft\Exchange
Server\V15\FrontEnd\HttpProxy\owa\auth\15.2.792. The installation cannot continue.
Any ideas to resolve the issue would be much appreciated.