The following error is seen after installing a Windows OS patch on the OneClick server:
"No SpectroSERVERS available"
Nothing else has changed in the environment.
Release: Any Spectrum release running on Windows
It is recommend the Windows patches be matching on the two OSs. In this case the OS patching did match.
The bigger problem was solved by a reboot of the SpectroSERVER after the OneClick came online. This caused communication to work correctly.