SIGABRT on OS X

My game works fine in the Editor and on Android, but when I test the standalone on OS X it sometimes crashes on startup. How should I go about debugging this?

Here's the error log:

 Receiving unhandled NULL exception
 Receiving unhandled NULL exception
 Receiving unhandled NULL exception
 Receiving unhandled NULL exception
 Obtained 0 stack frames.
 Obtained 0 stack frames.
 Obtained 15 stack frames.
 Stacktrace:
 
 
 Native stacktrace:
 
 Obtained 0 stack frames.
     0   libsystem_kernel.dylib              0x00007fff82e8d866 __pthread_kill + 10
     1   libsystem_c.dylib                   0x00007fff862e2b1a abort + 125
     2   BlockGame                           0x000000010041ffd4 _Z12HandleSignaliP9__siginfoPv + 36
     3   libmono.0.dylib                     0x0000000101ae925e mono_chain_signal + 71
     4   libmono.0.dylib                     0x0000000101a37bab mono_sigsegv_signal_handler + 213
     5   libsystem_platform.dylib            0x00007fff8e26c5aa _sigtramp + 26
     6   ???                                 0x00000001090cae14 0x0 + 4446793236
     7   ???                                 0x000000011252c215 0x0 + 4602380821
     8   ???                                 0x00000001119feed7 0x0 + 4590661335
     9   ???                                 0x00000001119f5406 0x0 + 4590621702
     10  ???                                 0x00000001119f4016 0x0 + 4590616598
     11  ???                                 0x000000010bf7546a 0x0 + 4495725674
     12  libmono.0.dylib                     0x0000000101a39757 mono_jit_runtime_invoke + 1788
     13  libmono.0.dylib                     0x0000000101b5c2db mono_runtime_invoke + 114
     14  libmono.0.dylib                     0x0000000101b61021 mono_runtime_delegate_invoke + 105
     15  libmono.0.dylib                     0x0000000101b873e0 start_wrapper + 534
     16  libmono.0.dylib                     0x0000000101bb6269 thread_start_routine + 211
     17  libmono.0.dylib                     0x0000000101bdc27c GC_start_routine + 99
     18  libsystem_pthread.dylib             0x00007fff84863899 _pthread_body + 138
     19  libsystem_pthread.dylib             0x00007fff8486372a _pthread_struct_init + 0
     20  libsystem_pthread.dylib             0x00007fff84867fc9 thread_start + 13
 * Assertion: should not be reached at mini-darwin.c:248
 
 
 Debug info from gdb:
 
 
 =================================================================
 Got a SIGABRT while executing native code. This usually indicates
 a fatal error in the mono runtime or one of the native libraries
 used by your application.
 =================================================================
 
 [1]    67142 abort      ./BlockGame