Load VS.NET class files in RTB pertaining syntax color?

[Pirate]

I tried this but it throw an error saying : "Invalid file format" .

Me.RichTextBox1.LoadFile("c:\a.cs", RichTextBoxStreamType.RichText)

but

when I try this , it works WITHOUT keywords color

Me.RichTextBox1.LoadFile("c:\a.cs", RichTextBoxStreamType.PlainText)

I need to load the file in RTB pertaining syntax coloring .

Anybody knows why it making that error ??

Thanks