Help me debug my C# API wrapper

I've been trying to write a C# class which wraps the USB-UIRT API. I'm a bit novice at all this and hoping that someone can help me get it working. The class file and a testbed file are linked below. The class compiles fine, is able to sucessfully open the API, but fails to transmit (GetLastWin32Error returns 0x57) or receive (learning provides some feedback, signal strength and frequency, but progress never goes above 0%).
Any help you could offer would be great!
The class file (ir.cs) and test harness (program.cs) are in this zip:
http://www.millercentral.com/usbuirt.zip
Thanks for any help you can provide!
-james
Any help you could offer would be great!
The class file (ir.cs) and test harness (program.cs) are in this zip:
http://www.millercentral.com/usbuirt.zip
Thanks for any help you can provide!
-james