I am working with ruby motion. As I had an issue when the app within the simulator did not want to scroll I re-installed x-code. The problem seemed to be resolved. Everything worked fine. However, suddenly the simulator would not open anymore with any app, providing different reasons.
So I deleted the application x-code again and re-installed it. (version 7.3(7D175)
I ran „bundle“ as well as rake pod:install and then rake.
The simulator would not open.
Reasons given in crashlog:
App 1 (this is the one which had worked before in the simulator):
"app was built for iOS 9.2 which is newer than this simulator 9.0"
Process: Lactase 2 
Path: /Users/USER/Library/Developer/CoreSimulator/Devices/91C530C5-CE00-457A-9DBD-EA95ABF0FBB0/data/Containers/Bundle/Application/F5FEF342-5AD5-4B3D-9940-24D9D2DEAFA5/Lactase 2.app/Lactase 2
Identifier: Lactase 2
Version: 1.0.7 (1.0.7)
Code Type: X86 (Native)
Parent Process: launchd_sim 
Responsible: Lactase 2 
User ID: 501
Date/Time: 2016-03-17 11:50:56.139 +0100
OS Version: Mac OS X 10.11.3 (15D21)
Report Version: 11
Anonymous UUID: 2349157F-CC76-5FE5-556C-A99898CF9E77
Sleep/Wake UUID: A44189DB-1F86-45D8-8A53-AF8F93C8BCCA
Time Awake Since Boot: 75000 seconds
System Integrity Protection: enabled
Crashed Thread: 0
Exception Type: EXC_BREAKPOINT (SIGTRAP)
Exception Codes: 0x0000000000000002, 0x0000000000000000
Exception Note: EXC_CORPSE_NOTIFY
Application Specific Information:
dyld: launch, loading dependent libraries
Dyld Error Message:
app was built for iOS 9.2 which is newer than this simulator 9.0
0x1000 - 0x946ff7 +com.nikolajandersen.lactase2 (1.0.7 - 1.0.7) <3043889D-4115-3C92-9664-BB59B91D04DF> /Users/USER/Library/Developer/CoreSimulator/Devices/91C530C5-CE00-457A-9DBD-EA95ABF0FBB0/data/Containers/Bundle/Application/F5FEF342-5AD5-4B3D-9940-24D9D2DEAFA5/Lactase 2.app/Lactase 2
0xecb000 - 0xeee377 +dyld_sim (360.19) <1A1E6A99-E860-37B8-BCEE-4B0A54ECCA01> /Library/Developer/CoreSimulator/Profiles/Runtimes/iOS 9.0.simruntime/Contents/Resources/RuntimeRoot/usr/lib/dyld_sim
0x8fe52000 - 0x8fe8658f dyld (360.19) <8F9518A3-884D-35FF-8FD9-FB149B7F1BF2> /usr/lib/dyld
I checked: The Simulator is Version 9.3 (SimulatorApp-645.9
App 2 (a different app which had also worked before in the simulator)
The reason provided for crashing is strange: It refers to a faulty code in the app. However, I had commented it out.
This is a link to the whole report.
What could be the reason for the problem? Should I delete not only the application x-code but also other files when re-installing?
Many thanks for helping, Daniel