Based on your previous question you used a debug build up until now. I'm guessing the release build is failing for you because it's obfuscated and doesn't contain debug information. Without further details I'll bet you have code such as getClass().getName()
or something of this type in your application that's causing this problem.
You need to connect the device with a cable and view the device logs with logcat or something similar. There you'll be able to get a stack trace to your specific error. You can de-obfuscate the stack trace using the mapping file from your build. Notice that this is VERY build specific. You can't use a mapping file from a different build...
Note that even an obfuscated Android stack trace is still relatively readable but if you want more... You would need the stack trace and the mapping file matching this EXACT version. Then follow these instructions.