glReadPixels crashes

I'm implementing glReadPixels attached to an orthographic camera. However, 3-5 seconds after the execution, Unity Editor crashes. I think it has something to do with the FrameBuffer or memory allocation Here it is my implementation:

onAwake():

 renderTex = new RenderTexture(20, 20, 20, RenderTextureFormat.ARGB32, RenderTextureReadWrite.Default);
 RenderTexture.active = renderTex;
 GetComponent<Camera>().targetTexture = renderTex;

onUpdate():

 information=new byte[20*20*4];
 unmanagedPointer = Marshal.AllocHGlobal(information.Length);
 Marshal.Copy(information, 0, unmanagedPointer, information.Length);
 
 GetComponent<Camera>().Render();
 Marshal.FreeHGlobal(unmanagedPointer);

onPostRender():

 glReadPixels (0, 0, 20, 20, GL_BGRA, GL_UNSIGNED_INT_8_8_8_8_REV, unmanagedPointer);

Crash report:

 6   libGPUSupport.dylib             0x00000001188a627d 
 gpulCheckForFramebufferIOSurfaceChanges + 54
 7   libGPUSupport.dylib             0x00000001188a6202 gldUpdateReadFramebuffer + 42
 8   GLEngine                        0x00007fff9247e01c gleUpdateReadFramebufferState + 425
 9   GLEngine                        0x00007fff923ac751 glReadPixels_Exec +