Device functions like Scanner will not work in the emulators. Scanner only works on a Motorola device, with the Moto Webkit. To do scanning on other devices you will need to either build an Native Extension to do the scanning on none Moto devices via a scanner or use the camera to read barcodes via the Barcode command
I had a similar problem, however I was using Window Mobile.
In RhoStudio, I changed the target platform to Windows Mobile 6.0, rather than Windows Mobile 6.5.3 (therefore I downgraded).
I also changed the build.yml to contain:
capabilities: - none
Keep in mind that what Glenn states about Moto... I am running on a Moto device...
The Scanner API will work on Windows Mobile Motorola Devices, the version doesn't matter, in theory it would run on anything from WM5 / CE5.0 and up.
I'd also back up what Glenn is saying about Scanner only running on Moto devices and the original poster should use the Barcode API for their HTC Android. In the next major version we'll be aligning our APIs across all devices.