Authorize install issue with GroupWise 18 on WS 2016

I'm trying to install GroupWise 18 on Windows server 2016 but cannot get past the "authorize install" step. I copy the gwadmin-ipc command and paste into a command prompt (admin). Gwadmin-ipc runs without error, I return to the install screen and most times it immediately displays another gwadmin-ipc command with a new token key. It makes no difference whether I double click on GroupWise Install on the desktop or, right click and choose "Run as Administrator". The server is current on updates other than the 2018-01 cumulative update which is producing a 0x80070020 error and which I'm still trying to resolve. The two issues may be related but I'm assuming they are not. A server reboot has not changed anything.

What am I overlooking here? Any suggestions appreciated.

TIA, John