rake failing when trying to open ios simulator

[stansongman]

I'm following the HelloRuby tutorial. I recently downgrated from El Capitan to Yosemite on my Mac Pro for many reasons. At any rate, my Xcode version is: Version 7.2.1 (7C1002) which should be right for Yosemite. Here's what happens. I get what you see below. This example works fine on my laptop (running El Capitan). Any thoughts? I'm thinking I should completely uninstall Xcode and reinstall from scratch, but otherwise I'm at a loss.

HelloMotion$ rake
Build ./build/iPhoneSimulator-9.2-Development
Create ./build/iPhoneSimulator-9.2-Development/HelloMotion.app/Info.plist
Simulate /Users/Stan/Dropbox/git/HelloMotion/build/iPhoneSimulator-9.2-Development/HelloMotion.app
2016-10-10 09:18:25.495 repl[621:6201] +[SimServiceContext sharedServiceContextForDeveloperDir:error:]: unrecognized selector sent to class 0x10afc68c8
2016-10-10 09:18:25.503 repl[621:6201] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '+[SimServiceContext sharedServiceContextForDeveloperDir:error:]: unrecognized selector sent to class 0x10afc68c8'
*** First throw call stack:
(
0 CoreFoundation 0x00007fff95b3d03c exceptionPreprocess + 172
1 libobjc.A.dylib 0x00007fff941b676e objc_exception_throw + 43
2 CoreFoundation 0x00007fff95b3ffad +[NSObject(NSObject) doesNotRecognizeSelector:] + 205
3 CoreFoundation 0x00007fff95a85e24 __forwarding + 1028
4 CoreFoundation 0x00007fff95a85998 _CF_forwarding_prep_0 + 120
5 repl 0x00000001093931f2 +[RMSimDevice defaultDeviceSet:] + 66
6 repl 0x00000001093a0c17 _Z17init_IOSSimulator19jit_bridge_config_t + 775
7 repl 0x00000001092f0609 main + 5289
8 libdyld.dylib 0x00007fff9b4a85c9 start + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException

The application terminated. A crash report file may have been generated by the
system, use rake crashlog' to open it. Userake debug=1' to restart the app

in the debugger.

rake aborted!
TypeError: no implicit conversion from nil to integer
/Library/RubyMotion/lib/motion/project/template/ios.rb:243:in exit' /Library/RubyMotion/lib/motion/project/template/ios.rb:243:inblock in <top (required)>'
Tasks: TOP => default => simulator
(See full trace by running task with --trace)
HelloMotion$