On attempting to install XCTU on Windows 8.1, I receive the message: ‘There is an instance of XCTU running. Please close all instances before continuing with the installation’.
There is no previous installation, and therefore no possibility of an instance running. The same happens either with normal installation as an unprivileged user, with admin credentials supplied when requested, or when attempting to install while logged in as admin. The file was downloaded from the Digi site as 40003026_A.exe
Joe
mare sure you didn’t rename 40003026_A.exe in xctu.exe 
Well done, actually it was something more complex than that, as I downloaded it on a different machine than it was to be installed, and before the parts arrived. I’d have forgotten what it was otherwise.
As if computers didn’t give us enough problems…