Add some debug output (using Debug.Log()) to see if a collision is actually occurring. If not, it’s probably a problem with your collision setup (e.g. colliders, etc.). If it is occurring, add debug output to see if the code inside the conditional is being executed. If it’s not, add debug output to display the tag associated with the other object to see if it’s what you’re expecting. If the code is being executed (which seems unlikely, given your description), then you can start trying to figure out why the score increase isn’t being reflected and so on.
I believe Unity 3 has some new debugging features, but if you’re using 2.x, Debug.Log() is pretty much the way to go, AFAIK at least. The process I described above can easily be generalized, and is how one goes about debugging problems like this in 2.x, more or less.
That errors doesn’t have to do with your Collision.
It looks that the editor is having an issue with a format of a RenderTarget, either internally or one that you output from your camera. If it’s Unity 3.0 it could be the Camera preview, but regardless that error is an internal Unity error and not based off your GamePlay (but maybe based off your assets).
The trick is when it says UnityEditor as the stacktrace, it means that it’s either an EditorScript or internal UnityEditor error and not something caused by Game Scripts.