Error support ios 64-bit

hi,everyone,
Build and run my project with Xcode 6.1.1 and Unity 5.0.0(b19) had something error.Like this:
error1:
Undefined symbols for architecture arm64:

"_System_System_Timers_Timer__CustomAttributeCache_System_System_Timers_Timer_Elapsed_EventInfo", referenced from:

System_System_Timers_Timer_Elapsed_EventInfo in Bulk_System_3.o

ld: symbol(s) not found for architecture arm64

clang: error: linker command failed with exit code 1 (use -v to see invocation)

error 2:
Undefined symbols for architecture armv7:

"_System_System_Timers_Timer__CustomAttributeCache_System_System_Timers_Timer_Elapsed_EventInfo", referenced from:

System_System_Timers_Timer_Elapsed_EventInfo in Bulk_System_3.o

ld: symbol(s) not found for architecture armv7

clang: error: linker command failed with exit code 1 (use -v to see invocation)


Someone have idea about that? Help me,Thank you

 

Thank you.
When i use the version of Unity 4.6.1p3, the error is gone. How strange.