If the Arduino is sending the data properly which can be verified via the use of the Serial Monitor, then the Arduino has done it's job.
Then it is absolutely a C# question.
I suspect that those folks at the C# forum have no freaking clue what an Arduino is!
Anyway, a C# question no matter how you slice it.
As I wrote above, I have written the Arduino code to send information out its serial port, and have a corresponding VB.NET program reading in that information.
.