After upgrading the core server from a previous version to 2017.3 the Remote Control might fail with "the signed rights document was not valid. authentication failed." for LANDesk Users, which are not LANDesk Administrators.
This is happening as 2017.3 uses different access for the folder C:\Program Files\LANDesk\Shared Files\keys on the core.
Adding the local group LANDesk Management Suite with Read & Execute, List Folder Contents and Read rights usually fixes this issue.