NullReferenceException: Object reference not set to an instance of an object. MaterialConfig.GetMaterialPropertyBlock (UnityEngine.Material mat, UnityEngine.Vector3 pos, UnityEngine.Vector3 scale) (at <00000000000000000000000000000000>:0) MaterialSetup.OnEnable () (at <00000000000000000000000000000000>:0) GameManager.CreatePrefab (System.String strPrefab, UnityEngine.Vector3 pos, UnityEngine.Quaternion rot, UnityEngine.Vector3 scale, System.Boolean active) (at <00000000000000000000000000000000>:0) Prefab.Spawn (UnityEngine.Vector3 pos, UnityEngine.Quaternion rot, UnityEngine.Vector3 scale, System.Boolean active) (at <00000000000000000000000000000000>:0) World.Spawn (System.String category, Prefab prefab, UnityEngine.Vector3 position, UnityEngine.Quaternion rotation, UnityEngine.Vector3 scale) (at <00000000000000000000000000000000>:0) World.Spawn (ProtoBuf.PrefabData prefab) (at <00000000000000000000000000000000>:0) World+<Spawn>d__71.MoveNext () (at <00000000000000000000000000000000>:0) WorldSetup+<InitCoroutine>d__15.MoveNext () (at <00000000000000000000000000000000>:0) UnityEngine.SetupCoroutine.InvokeMoveNext (System.Collections.IEnumerator enumerator, System.IntPtr returnValueAddress) (at <00000000000000000000000000000000>:0) GameManager:CreatePrefab(String, Vector3, Quaternion, Vector3, Boolean) Prefab:Spawn(Vector3, Quaternion, Vector3, Boolean) World:Spawn(String, Prefab, Vector3, Quaternion, Vector3) World:Spawn(PrefabData) <Spawn>d__71:MoveNext() <InitCoroutine>d__15:MoveNext() UnityEngine.SetupCoroutine:InvokeMoveNext(IEnumerator, IntPtr)
*.*.*.*:55127/76561############/adan disconnecting: Exception (cs:82035): NullReferenceException: Object reference not set to an instance of an object. MaterialConfig.GetMaterialPropertyBlock (UnityEngine.Material mat, UnityEngine.Vector3 pos, UnityEngine.Vector3 scale) (at <00000000000000000000000000000000>:0) MaterialSetup.OnEnable () (at <00000000000000000000000000000000>:0) GameManager.CreatePrefab (System.String strPrefab, UnityEngine.Vector3 pos, UnityEngine.Quaternion rot, UnityEngine.Vector3 scale, System.Boolean active) (at <00000000000000000000000000000000>:0) Prefab.Spawn (UnityEngine.Vector3 pos, UnityEngine.Quaternion rot, UnityEngine.Vector3 scale, System.Boolean active) (at <00000000000000000000000000000000>:0) World.Spawn (System.String category, Prefab prefab, UnityEngine.Vector3 position, UnityEngine.Quaternion rotation, UnityEngine.Vector3 scale) (at <00000000000000000000000000000000>:0) World.Spawn (ProtoBuf.PrefabData prefab) (at <00000000000000000000000000000000>:0) World+<Spawn>d__71.MoveNext () (at <00000000000000000000000000000000>:0) WorldSetup+<InitCoroutine>d__15.MoveNext () (at <00000000000000000000000000000000>:0) UnityEngine.SetupCoroutine.InvokeMoveNext (System.Collections.IEnumerator enumerator, System.IntPtr returnValueAddress) (at <00000000000000000000000000000000>:0) GameManager:CreatePrefab(String, Vector3, Quaternion, Vector3, Boolean) Prefab:Spawn(Vector3, Quaternion, Vector3, Boolean) World:Spawn(String, Prefab, Vector3, Quaternion, Vector3) World:Spawn(PrefabData) <Spawn>d__71:MoveNext() <InitCoroutine>d__15:MoveNext() UnityEngine.SetupCoroutine:InvokeMoveNext(IEnumerator, IntPtr)     what error this

Are you using a custom map? If so which one?

I'm getting this exact same error. This is a procedural map that I've modified in Rust Edit, dropping in a few free and paid prefabs I've collected.

What was your solution and how was it resolved ?

I was able to resolve my issue by deleting the prefab Rock Splash A that was a part of one of the monuments I was using. Hope this helps you as well.