objective c - Symbol not found objc class reference -

"_objc_class_$_inputamountvc", referenced from:  objc-class-ref-to-inputamountvc in p0931917_prac_2appdelegate.o  ld: symbol(s) not found collect2: ld returned 1 exit status  ld "build/debug-iphonesimulator/p0931917 prac 2.app/p0931917 prac 2" normal i386 cd "/volumes/storage/p0931917 prac 2" setenv macosx_deployment_target 10.6 setenv path "/developer/platforms/iphonesimulator.platform/developer/usr/bin:/developer/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin" /developer/platforms/iphonesimulator.platform/developer/usr/bin/gcc-4.2 -arch i386 -isysroot /developer/platforms/iphonesimulator.platform/developer/sdks/iphonesimulator4.3.sdk "-l/volumes/storage/p0931917 prac 2/build/debug-iphonesimulator" "-f/volumes/storage/p0931917 prac 2/build/debug-iphonesimulator" -filelist "/volumes/storage/p0931917 prac 2/build/p0931917 prac 2.build/debug-iphonesimulator/p0931917 prac 2.build/objects-normal/i386/p0931917 prac 2.linkfilelist" -mmacosx-version-min=10.6 -xlinker -objc_abi_version -xlinker 2 -framework foundation -framework uikit -framework coregraphics -o "/volumes/storage/p0931917 prac 2/build/debug-iphonesimulator/p0931917 prac 2.app/p0931917 prac 2"  dyld: shared cached file build against different libsystem.dylib, ignoring cache dyld: shared cached file build against different libsystem.dylib, ignoring cache dyld: shared cached file build against different libsystem.dylib, ignoring cache dyld: shared cached file build against different libsystem.dylib, ignoring cache dyld: shared cached file build against different libsystem.dylib, ignoring cache undefined symbols:   "_objc_class_$_inputamountvc", referenced from:       objc-class-ref-to-inputamountvc in p0931917_prac_2appdelegate.o ld: symbol(s) not found collect2: ld returned 1 exit status 

i'm having error please help.

the linker doesn't find object code (binary) particular class.

if code, make sure have .m/.mm/.c/.cpp source file belong target building.

if in library, make sure linker can find (library search path etc.) , build same settings.

the latter paragraph dyld looks problem that: dyld build against version of libsystem.dylib current target, doesn't have code need in it. (other architecture or base sdk?)