XCode USB Development on 64bit. Writepipe Failing to send data

Hi,

I'm using writepipe for data transfer to my custom HID device on USB. When I build the app in Xcode on OSX Lion and boot my Mac in 32 bit mode then the HID data transfer with writepipe works fine. But when I boot my Mac in 64 bit mode and run my app in XCode writepipe returns with errors "404f" and "2ed".

I've had a various look at other forums and there's nothing out there helpful. Why would writepipe work in 32 bit mode but not in 64 bit mode?

Are there alternatives to writepipe? I don't want to get a USB analyzer to see what the data is doing. Is this a timing issue if so what does Lion 64 bit do different to Lion 32 bit?

Regards,

Saj