Receive a crash prompt saying: "Moving File Failed - Moving Temp/Assembly-CSharp.dll.mdb to Library/ScriptAssemblies/....Access is denied" when debugging.

Repro:
1) Create a script with the following code. Note the Debug.Log is commented out.

```
using UnityEngine;
public class TestScript : MonoBehaviour {
void Start () {
// Debug.Log ("Start"); // breakpoint here
}
}
```

2) Place a breakpoint on the commented line. It will automatically move to the next line, that is expected. Attach MonoDevelop to the Editor.
3) Enter playmode in the Editor. The debugger will stop at the end of the Start function.
4) Press the continue button in MonoDevelop. Don't switch to Unity just yet.
5) Uncomment the commented line. Save your changes.
6) Switch back to Unity. At this point Unity will try to compile the code and will throw the "Moving file failed message"