Recently came across this error and found solution so thought of sharing this.
Scenario: Running xaml file from UiRobot.exe from cmd line
UiRobot.exe -f main.xaml
Error : I was getting License permission missing: Trigger
and searched the forum got this link https://orchestrator.uipath.com/v2018.3/docs/frequently-encountered-orchestrator-errors#section--system-runtime-interopservices-comexception-licence-permission-missing-
then came to know that there is issue with UiPath.UIAutomation.Activities
If you have projects created with Studio v2018.3.1 which were using the
UiPath.UIAutomation.Activitiesdependency version 18.3.6864.20582 you must open them in Studio and the
UiPath.UIAutomation.Activitiesdependency must be updated to the 18.3.6877.28298 version.
then i updated my UiPath.UIAutomation.Activities version Hurray it worked.
Hope this helps anyone looking for solution.