There seems to be some kind of problem with saving in 1.4.0, but I struggle to get this error myself. I've uploaded a version (1.4.0c) that lets you copy the full error, which I need to identify the issue.
I have fantastic news! I have gotten the error in your new build. (location: Silverpine, spring season) Here it is:
System.NullReferenceException: Object reference not set to an instance of an object.
at TypeSerializationUtility.SerializeWithType (ISerializable serializable, System.IO.BinaryWriter binaryWriter) [0x00000] in <00000000000000000000000000000000>:0
at RoutineArgument_SeekPlayerAndTalk.Serialize (System.IO.BinaryWriter binaryWriter) [0x00000] in <00000000000000000000000000000000>:0
at TypeSerializationUtility.SerializeListWithType[T] (System.Collections.Generic.List`1[T] list, System.IO.BinaryWriter binaryWriter) [0x00000] in <00000000000000000000000000000000>:0
at NPCRoutine.Serialize (System.IO.BinaryWriter binaryWriter) [0x00000] in <00000000000000000000000000000000>:0
at WalkUpManager.Serialize (System.IO.BinaryWriter binaryWriter) [0x00000] in <00000000000000000000000000000000>:0
at SerializationManager.SerializePersistent () [0x00000] in <00000000000000000000000000000000>:0
at SerializationManager.Save (System.String saveFileName) [0x00000] in <00000000000000000000000000000000>:0
at SaveUI.Save (System.Int32 saveSlot) [0x00000] in <00000000000000000000000000000000>:0
at SaveUI+<AutosaveCoroutine>d__29.MoveNext () [0x00000] in <00000000000000000000000000000000>:0
at UnityEngine.SetupCoroutine.InvokeMoveNext (System.Collections.IEnumerator enumerator, System.IntPtr returnValueAddress) [0x00000] in <00000000000000000000000000000000>:0
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I also got an additional one outside of Silverpine (Sending this too because it's distinct):
System.NullReferenceException: Object reference not set to an instance of an object.
at TypeSerializationUtility.SerializeWithType (ISerializable serializable, System.IO.BinaryWriter binaryWriter) [0x00000] in <00000000000000000000000000000000>:0
at RoutineArgument_SeekPlayerAndTalk.Serialize (System.IO.BinaryWriter binaryWriter) [0x00000] in <00000000000000000000000000000000>:0
at TypeSerializationUtility.SerializeListWithType[T] (System.Collections.Generic.List`1[T] list, System.IO.BinaryWriter binaryWriter) [0x00000] in <00000000000000000000000000000000>:0
at NPCRoutine.Serialize (System.IO.BinaryWriter binaryWriter) [0x00000] in <00000000000000000000000000000000>:0
at WalkUpManager.Serialize (System.IO.BinaryWriter binaryWriter) [0x00000] in <00000000000000000000000000000000>:0
at SerializationManager.SerializePersistent () [0x00000] in <00000000000000000000000000000000>:0
at SerializationManager.Save (System.String saveFileName) [0x00000] in <00000000000000000000000000000000>:0
at SaveUI.Save (System.Int32 saveSlot) [0x00000] in <00000000000000000000000000000000>:0
at UnityEngine.Events.UnityEvent.Invoke () [0x00000] in <00000000000000000000000000000000>:0
at UnityEngine.EventSystems.ExecuteEvents.Execute[T] (UnityEngine.GameObject target, UnityEngine.EventSystems.BaseEventData eventData, UnityEngine.EventSystems.ExecuteEvents+EventFunction`1[T1] functor) [0x00000] in <00000000000000000000000000000000>:0
at UnityEngine.EventSystems.StandaloneInputModule.ReleaseMouse (UnityEngine.EventSystems.PointerEventData pointerEvent, UnityEngine.GameObject currentOverGo) [0x00000] in <00000000000000000000000000000000>:0
at UnityEngine.EventSystems.StandaloneInputModule.ProcessMousePress (UnityEngine.EventSystems.PointerInputModule+MouseButtonEventData data) [0x00000] in <00000000000000000000000000000000>:0
at UnityEngine.EventSystems.StandaloneInputModule.ProcessMouseEvent (System.Int32 id) [0x00000] in <00000000000000000000000000000000>:0
at UnityEngine.EventSystems.StandaloneInputModule.Process () [0x00000] in <00000000000000000000000000000000>:0
at UnityEngine.EventSystems.EventSystem.Update () [0x00000] in <00000000000000000000000000000000>:0
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Update: The longer error is sent when I try to manually save (regardless of location) and the shorter error is sent when the game autosaves (regardless of location)
Thanks. I would release a patch for this, but simply waiting for 24 hours after loading the offending 1.3.2 save fixes it, since it clears out the thing that's preventing the game from saving properly.
This is also unrelated to the bug you encountered in 1.3.2, which is caused by something outside of the town. If you see it again, feel free to post the full error for that one too.