SetNeighbour() Issues

I'm currently attempting to set a grid of neighboring terrain's LOD to match, and having serious troubles. I don't usually ask for help, but here goes. When I run the following code, Unity completely crashes with an Access Violation (0xc0000005):

Code (csharp):

1.         // set neighbours, find for painting
2.         //setup raycast values
3.         for (int a = 0; a < 5; a++)
4.         {
5.             Terrain[] terrainNeighbours = new Terrain[5];
6.             RaycastHit[] neighbourRays = new RaycastHit[5];
7.  
8.             float xShift = 250;
9.             float zShift = 250;
10.             //shift loop position
11.             if(a == 0)
12.             {
13.                 zShift = -250;
14.             }
15.             if(a == 1)
16.             {
17.                 xShift = 750;
18.             }
19.             if(a == 2)
20.             {
21.                 zShift = 750;
22.             }
23.             if(a == 3)
24.             {
25.                 xShift = -250;
26.             }
27.             Vector3 neighbourBasePosition = new Vector3(modifiedTerrain.transform.position.x + xShift,modifiedTerrain.transform.position.y,modifiedTerrain.transform.position.z + zShift);
28.             //setup raycast values
29.             int layerMaskPrimary = 1 << 8;
30.             int layerMaskSecondary = 1 << 9;
31.             int layerMask = layerMaskPrimary | layerMaskSecondary;
32.  
33.             Physics.Raycast(new Vector3(neighbourBasePosition.x,50000,neighbourBasePosition.z), Vector3.down, out neighbourRays[4], 100000, layerMask);
34.             Physics.Raycast(new Vector3(neighbourBasePosition.x - 500,50000,neighbourBasePosition.z), Vector3.down, out neighbourRays[0], 100000, layerMask);
35.             Physics.Raycast(new Vector3(neighbourBasePosition.x,50000,neighbourBasePosition.z + 500), Vector3.down, out neighbourRays[1], 100000, layerMask);
36.             Physics.Raycast(new Vector3(neighbourBasePosition.x + 500,50000,neighbourBasePosition.z), Vector3.down, out neighbourRays[2], 100000, layerMask);
37.             Physics.Raycast(new Vector3(neighbourBasePosition.x,50000,neighbourBasePosition.z - 500), Vector3.down, out neighbourRays[3], 100000, layerMask);
38.  
39.             for(int n = 0; n < neighbourRays.Length; n++)
40.             {
41.                 if(neighbourRays[n].collider)
42.                 {
43.                     terrainNeighbours[n] = neighbourRays[n].collider.gameObject.GetComponent<Terrain>();
44.                 }
45.             }
46.             //set terrain array
47.             if(terrainNeighbours[4] != null)
48.             {
49.                 terrainNeighbours[4].SetNeighbors(terrainNeighbours[0],terrainNeighbours[1],terrainNeighbours[2],terrainNeighbours[3]); // set neighbours
50.                 terrainNeighbours[4].basemapDistance = 1500;
51.                 terrainNeighbours[4].Flush();
52.                 terrainNeighbours[4].heightmapPixelError = 0.0f;
53.             }
54.         }

I can get it to avoid crashing by adding the line:

Code (csharp):

1.                     terrainNeighbours[n].SetNeighbors(null,null,null,null); // set neighbours

In the collider for loop, but obviously this is counterintuitive as it basically resets the neighboring I'm trying to achieve. Any help would be much appreciated.