incompatibility with high-res-screenshot code

see the pic to show the screenshots another guy and myself are getting from the high res screenshot code recently. the grey color is the same as the hierarchy background.

it seems the script works on some installs of Unity3d and not on other, maybe 3.55?

 using UnityEngine;
 using System.Collections;
 
 public class HiResScreenShots : MonoBehaviour {
     public int resWidth = 2550; 
     public int resHeight = 3300;
 
     private bool takeHiResShot = false;
 
     public static string ScreenShotName(int width, int height) {
         return string.Format("{0}/screenshots/screen_{1}x{2}_{3}.png", 
                              Application.dataPath, 
                              width, height, 
                              System.DateTime.Now.ToString("yyyy-MM-dd_HH-mm-ss"));
     }
 
     public void TakeHiResShot() {
         takeHiResShot = true;
     }
 
     void LateUpdate() {
         takeHiResShot |= Input.GetKeyDown("k");
         if (takeHiResShot) {
             RenderTexture rt = new RenderTexture(resWidth, resHeight, 24);
             camera.targetTexture = rt;
             Texture2D screenShot = new Texture2D(resWidth, resHeight, TextureFormat.RGB24, false);
             camera.Render();
             RenderTexture.active = rt;
             screenShot.ReadPixels(new Rect(0, 0, resWidth, resHeight), 0, 0);
             camera.targetTexture = null;
             RenderTexture.active = null; // JC: added to avoid errors
             Destroy(rt);
             byte[] bytes = screenShot.EncodeToPNG();
             string filename = ScreenShotName(resWidth, resHeight);
             System.IO.File.WriteAllBytes(filename, bytes);
             Debug.Log(string.Format("Took screenshot to: {0}", filename));
             takeHiResShot = false;
         }
     }
 }