The coordinate systems cannot be selected because the dialog 'Projections' displays neither folders nor projection files (*.PRJ).
Sometimes it happens that no projection files are copied to the folder: c:\Users\%USERNAME%\AppData\Roaming\PTV Vision\PTV Visum 18\Projections\
You can easily correct this by copying the contents of the folder c:\Program Files\PTV Vision\PTV Visum 18\Exe\Projections\ to c:\Users\%USERNAME%\AppData\Roaming\PTV Vision\PTV Visum 18\Projections\
While running the setup, the projection files are copied to the EXE folder, to which normal user accounts do not have any access. Starting Visum, it is checked whether the current user already has a projections folder. Each user gets his own folder, thus can delete non-used projections or add additional projections.
If the list of projections is empty, the folder 'Projections' does exist, but is empty. You can delete this folder and start Visum again. This triggers an attempt to copy the projection files. If the folder remains empty, you can copy the files manually.