Hello Hardy Wang,
Sorry for the trouble converting your LINQ code. Currently, the Code Converter does not well handle LINQ, though we hope it will improve in the future (with improvements to the underlying NRefactory open source engine). For most other C#/VB, the Code Converter should be able to help you convert between the syntaxes.
If you'd like , you can share an example of the LINQ you're trying to convert and we'll use that as reference test for future engine improvements.