This method has the standard behavior when this object has been created using the standard constructors. Otherwise, it uses "currentToken" and "expectedTokenSequences" to generate a parse error message and returns it. If this object has been created due to a parse error, and you do not catch it (it gets thrown from the parser), then this method is called during the printing of the final stack trace, and hence the correct error message gets displayed.
ParseException Class | Lucene.Net.QueryParsers Namespace