Issue

Autodesk made a breaking, albeit vaguely documented, change in the Revit 2018 API that causes legacy applications to throw an exception when the user attempts to place family instances.  This adversely affects the Add Points-Planar Face command in ElumTools 2018.1.

Solution

Update ElumTools to version 2018.2 or later.

Error Message

Could not complete ElumTools command:  AddCalcPointsFaceCommand

Exception:
Autodesk.Revit.Exceptions.OperationCanceledException: The user aborted the pick operation.
   at Autodesk.Revit.UI.UIDocument.PromptForFamilyInstancePlacementInternal(FamilySymbol familySymbol, PromptForFamilyInstancePlacementOptions options)
   at ElumTools.AddCalcPointsFaceCommand.PlaceNewInstances(FamilySymbol symbol)
   at ElumTools.AddCalcPointsFaceCommand.Execute()
   at ElumTools.ElumToolsCommand.ExecuteCommand(String& message, ElementSet elements)
   at ElumTools.ElumToolsCommand.ExecuteInternal(String& message, ElementSet elements)
   at ElumTools.ElumToolsCommand.ExecuteTransaction(ExternalCommandData commandData, String& message, ElementSet elements)
   at ElumTools.ElumToolsCommand.Execute(ExternalCommandData commandData, String& message, ElementSet elements)

ElumTools 2018 Release 1 (2018.1.0.4)
RevitAPIUI
18.0.0.0
18.0.1.2

C:\Program Files\Autodesk\Revit 2018\RevitAPIUI.dll