System.ArgumentNullException at Orts.Viewer3D.SoundStream.Interpolate (1.3.1.4328, Mideast UK 2.0 Steam Era, RS_The Down Scotch Goods)

I'm trying to run the activity RS_The Down Scotch Goods.act on the MEUK Steam route v2.0.

The progress bar get right to the rns and the sound starts but the OR window closes and another window opens containing
"Error: System.ArgumentNullException: Value cannot be null.
Parameter name: source
at System.Linq.Enumerable.Count[TSource](IEnumerable`1 source)
at Orts.Viewer3D.SoundStream.Interpolate(Single x, VolumeCurve Curve) in E:\Documents\Coding\Jenkins\jobs\Open Rails Stable\workspace\Source\RunActivity\Viewer3D\Sound.cs:line 1342
at Orts.Viewer3D.SoundStream.SetFreqAndVolume() in E:\Documents\Coding\Jenkins\jobs\Open Rails Stable\workspace\Source\RunActivity\Viewer3D\Sound.cs:line 1320
at Orts.Viewer3D.SoundStream.Update() in E:\Documents\Coding\Jenkins\jobs\Open Rails Stable\workspace\Source\RunActivity\Viewer3D\Sound.cs:line 1275
at Orts.Viewer3D.SoundSource.Update() in E:\Documents\Coding\Jenkins\jobs\Open Rails Stable\workspace\Source\RunActivity\Viewer3D\Sound.cs:line 935
at Orts.Viewer3D.Processes.SoundProcess.Sound() in E:\Documents\Coding\Jenkins\jobs\Open Rails Stable\workspace\Source\RunActivity\Viewer3D\Processes\SoundProcess.cs:line 132
at Orts.Viewer3D.Processes.SoundProcess.DoSound() in E:\Documents\Coding\Jenkins\jobs\Open Rails Stable\workspace\Source\RunActivity\Viewer3D\Processes\SoundProcess.cs:line 116
at Orts.Viewer3D.Processes.SoundProcess.SoundThread() in E:\Documents\Coding\Jenkins\jobs\Open Rails Stable\workspace\Source\RunActivity\Viewer3D\Processes\SoundProcess.cs:line 100
at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Threading.ThreadHelper.ThreadStart()"

I've attached the log file.