Poked around in this forum and found the topic "Preparing JRiver Media Center for Remote Control".
There I found:
1. From the top toolbar select «Tools», then from the drop down list, select «Options».
As a shortcut, you may use «CTRL-O» on windows and «CMD-O» on MAC.
2. From the options window, select «Media Network» from the left menu. You will now be presented with various options related to DLNA and library sharing.
3. Make sure that the first option is selected: «Use Media Network to share this library and enable DLNA». Once selected, you are presented with a configuration wizard.
When I followed these steps the configuration wizard notified me that my firewall was not set to allow MC access and offered to set it for me. When I did that I got a strange error message but after that my Android JRemote started working.