I came across this less than helpful error message while standardizing IP schemes on our Micros systems. The cause actually had nothing to do with encryption at all, but IP address mismatches.
Here are some things to check/try if you get this error.
Make sure the IP address of your server matches the IP you have set in Network Nodes.
Make sure the entries in the Windows host file, C:\WINDOWS\system32\drivers\etc\hosts, matches the names/addresses in Network Nodes.
Open \MICROS\Common\Etc\MDSHosts.xml in notepad and make sure the names/addresses are correct.
Open \MICROS\Res\CAL\<your WS type>\Packages\WS4RES\Micros\Etc\MDSHosts.xml and make sure the names/addresses are correct.
Whenever you make changes in Network Nodes all of the files above should be updated, but that isn't always the case. If the MDSHost.xml file that your system uses isn't updated your workstations will be looking at the wrong IP address for the server, and for some reason Micros decided that should throw an encryption error.