SerialPort1.Write(ChrW(10))
Disclaimer: I haven't touched Visual Basic since Microsoft called for a complete language do-over after 6.0. After the .NET makeover, it was just too hideous to stomach anymore.
So, maybe I'm jumping to conclusions here, but from that line it looks like you might be sending WIDE characters.
Wide characters are Unicode-style 16-bit (2-byte) characters. Your Arduino sketch is expecting a single-byte (8-bit) char.