ArgumentOutOfRangeException occurs when Mode is Advanced?
If yes, then this is a known issue on the EasyRoads side.
Raoul (the creator of EasyRoads) wrote that this issue has been fixed and I have confirmation of this from the user who originally reported it.
So try updating EasyRoads using the Asset Store.

ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index

I have now installed the 3d road package, the demo and the hd textures.
I am now having a problem trying to get the right road types. 

initial error... no  easyroads3d detected by  real world terrains.

i tried importing that new package Attachment icon RWT v4.4.1 - EasyRoads3D v3.1.9 fix.unitypackage

InfinityCode.RealWorldTerrain.Editors.RealWorldTerrainContainerEditor.DrawBaseDist () (at Assets/Infinity Code/Real World Terrain/Scripts/Editor/Editors/RealWorldTerrainContainerEditor.cs:80)
InfinityCode.RealWorldTerrain.Editors.RealWorldTerrainContainerEditor.OnInspectorGUI () (at Assets/Infinity Code/Real World Terrain/Scripts/Editor/Editors/RealWorldTerrainContainerEditor.cs:402)
UnityEditor.UIElements.InspectorElement+<>c__DisplayClass58_0.<CreateIMGUIInspectorFromEditor>b__0 () (at <1fe7a3c0284a456b9681b7a93141c89a>:0)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)

Thank you for bug report.
Raoul renamed one of the resources in EasyRoads3D v3.1.9.
Fix for RWT v4.4.1 is attached.

Thanks for the quick response, works great now.

Though the error message is different from OP's. Here it is:

The Object you want to instantiate is null.
  at UnityEngine.Object.CheckNullArgument (System.Object arg, System.String message) [0x00008] in C:\buildslave\unity\build\Runtime\Export\Scripting\UnityEngineObject.bindings.cs:374 
  at UnityEngine.Object.Instantiate (UnityEngine.Object original) [0x00007] in C:\buildslave\unity\build\Runtime\Export\Scripting\UnityEngineObject.bindings.cs:231 
  at InfinityCode.RealWorldTerrain.Generators.RealWorldTerrainEasyRoads3DGenerator.Init () [0x0003a] in C:\Users\Eric\Documents\Unity Projects\Real World\Assets\Infinity Code\Real World Terrain\Scripts\Editor\Generators\RealWorldTerrainEasyRoads3DGenerator.cs:267 
  at InfinityCode.RealWorldTerrain.Generators.RealWorldTerrainRoadGenerator.Init (InfinityCode.RealWorldTerrain.RealWorldTerrainContainer container) [0x00133] in C:\Users\Eric\Documents\Unity Projects\Real World\Assets\Infinity Code\Real World Terrain\Scripts\Editor\Generators\RealWorldTerrainRoadGenerator.cs:248 
  at InfinityCode.RealWorldTerrain.Generators.RealWorldTerrainRoadGenerator.Generate (InfinityCode.RealWorldTerrain.RealWorldTerrainContainer container) [0x00001] in C:\Users\Eric\Documents\Unity Projects\Real World\Assets\Infinity Code\Real World Terrain\Scripts\Editor\Generators\RealWorldTerrainRoadGenerator.cs:194 
  at InfinityCode.RealWorldTerrain.Phases.RealWorldTerrainGenerateRoadsPhase.Enter () [0x00001] in C:\Users\Eric\Documents\Unity Projects\Real World\Assets\Infinity Code\Real World Terrain\Scripts\Editor\Phases\RealWorldTerrainGenerateRoadsPhase.cs:18 
  at InfinityCode.RealWorldTerrain.Windows.RealWorldTerrainWindow.Update () [0x00011] in C:\Users\Eric\Documents\Unity Projects\Real World\Assets\Infinity Code\Real World Terrain\Scripts\Editor\Windows\RealWorldTerrainWindow.cs:418 
UnityEngine.Debug:LogError(Object)
InfinityCode.RealWorldTerrain.Windows.RealWorldTerrainWindow:Update() (at Assets/Infinity Code/Real World Terrain/Scripts/Editor/Windows/RealWorldTerrainWindow.cs:422)
UnityEditor.EditorApplication:Internal_CallUpdateFunctions() (at C:/buildslave/unity/build/Editor/Mono/EditorApplication.cs:303)

This is a known issue in EasyRoads3D v3.1.7.
As far as I know, Raoul (EasyRoads3D developer) has already fixed this problem.
Solution: Use a different version of EasyRoads3D.
The latest version in Asset Store is EasyRoads3D v3.1.8f2.

A road network is created in the Hierarchy but no roads are placed in the world, just one road object without any mesh at 0,0,0, and I get this error message:

Object reference not set to an instance of an object
  at EasyRoads3Dv3.ERRoad.Refresh () [0x00001] in <69cf1a9e593e4f2ca7976a517a06d72c>:0

  at EasyRoads3Dv3.ERRoad.SetWidth (System.Single width) [0x0001e] in <69cf1a9e593e4f2ca7976a517a06d72c>:0

  at EasyRoads3Dv3.ERRoadNetwork.CreateRoad (System.String roadName, EasyRoads3Dv3.ERRoadType roadType, UnityEngine.Vector3[] markers) [0x0002a] in <69cf1a9e593e4f2ca7976a517a06d72c>:0

  at InfinityCode.RealWorldTerrain.Generators.RealWorldTerrainRoadGenerator.CreateEasyRoads () [0x000d5] in C:\Depot\Assets\Infinity Code\Real World Terrain\Scripts\Editor\Generators\RealWorldTerrainRoadGenerator.cs:235

  at InfinityCode.RealWorldTerrain.Generators.RealWorldTerrainRoadGenerator.Generate (InfinityCode.RealWorldTerrain.RealWorldTerrainContainer container) [0x00597] in C:\Depot\Assets\Infinity Code\Real World Terrain\Scripts\Editor\Generators\RealWorldTerrainRoadGenerator.cs:467

  at InfinityCode.RealWorldTerrain.Phases.RealWorldTerrainGenerateRoadsPhase.Enter () [0x00001] in C:\Depot\Assets\Infinity Code\Real World Terrain\Scripts\Editor\Phases\RealWorldTerrainGenerateRoadsPhase.cs:18

  at InfinityCode.RealWorldTerrain.Windows.RealWorldTerrainWindow.Update () [0x00011] in C:\Depot\Assets\Infinity Code\Real World Terrain\Scripts\Editor\Windows\RealWorldTerrainWindow.cs:433
UnityEngine.Debug:LogError(Object)
InfinityCode.RealWorldTerrain.Windows.RealWorldTerrainWindow:Update() (at Assets/Infinity Code/Real World Terrain/Scripts/Editor/Windows/RealWorldTerrainWindow.cs:437)
UnityEditor.EditorApplication:Internal_CallUpdateFunctions()