How do I specifically see errors that happen in the CLIPS engine?

There are several ways, actually. One can be directly reading what the engine reports on TraceStream and ErrorStream, by explicitly using their Read() method. The easiest way I have found (it's time consuming, though) is to clips.DebugConfig.WatchAll() to activate all trace output and clips.DebugConfig.DribbleOn("my_trace.log"). When an error occurs in CLIPS, everything about it will be written to the file specified in DebugConfig.DribbleOn(), and it becomes easier to spot it correctly.