I'm getting the exact same error here. It happens all the time on the device, while everything runs just fine on the simulator.
I'll try to pinpoint the problem on my side. Really need this to work!
$ rake device --trace
** Invoke pixate:sass (first_time)
** Execute pixate:sass
sass sass/default.scss resources/default.css
** Invoke device (first_time)
** Invoke archive (first_time)
** Invoke build:device (first_time)
** Execute build:device
** Execute archive
** Execute device
XCODE_DIR="/Applications/Xcode.app/Contents/Developer" /Library/RubyMotion/bin/ios/deploy -d "4dea17ea83b2622755b98c3feffebacexxxxxxxx" "./build/iPhoneOS-6.0-Development/NoReceipt.ipa"
log: subscribing to device notification
log: found usb mobile device 4dea17ea83b2622755b98c3feffebace39c06fee
log: connecting to device
log: pairing device
log: creating lockdown session
log: starting file copy service
log: starting installer proxy service
log: opening file copy connection
log: creating staging directory
log: opening remote package path
log: writing data
log: closing remote package path
log: sending install command
log: progress report: 5% status: CreatingStagingDirectory
log: progress report: 15% status: ExtractingPackage
log: progress report: 20% status: InspectingPackage
log: progress report: 20% status: TakingInstallLock
log: progress report: 30% status: PreflightingApplication
log: progress report: 30% status: InstallingEmbeddedProfile
log: progress report: 40% status: VerifyingApplication
log: progress report: 50% status: CreatingContainer
log: progress report: 60% status: InstallingApplication
log: progress report: 70% status: PostflightingApplication
log: progress report: 80% status: SandboxingApplication
log: progress report: 90% status: GeneratingApplicationMap
log: progress report: 100% status: Complete
log: package has been successfully installed on device
Assertion failed: (product_version != nil), function start_debug_server, file deploy.m, line 483.