请帮我解决这个错误...
在设备上运行时出现此错误，但在模拟器上运行时，应用程序运行顺利且没有错误。
我有以下错误...
请帮我
Ld /Users/vipalpanchal/Library/Developer/Xcode/DerivedData/iRealify-hkospzktmsronzeeoslnvwfniaok/Build/Products/Debug-iphoneos/MySMSFriend.app/MySMSFriend normal armv7s
cd "/iTune/SMS Final App/SMS/MySMSFriend"
setenv IPHONEOS_DEPLOYMENT_TARGET 4.3
setenv PATH "/Applications/Xcode 2.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin:/Applications/Xcode 2.app/Contents/Developer/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin"
"/Applications/Xcode 2.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang" -arch armv7s -isysroot "/Applications/Xcode 2.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS6.1.sdk" -L/Users/vipalpanchal/Library/Developer/Xcode/DerivedData/iRealify-hkospzktmsronzeeoslnvwfniaok/Build/Products/Debug-iphoneos "-L/iTune/SMS Final App/SMS/MySMSFriend/Classes/Start" -F/Users/vipalpanchal/Library/Developer/Xcode/DerivedData/iRealify-hkospzktmsronzeeoslnvwfniaok/Build/Products/Debug-iphoneos -filelist /Users/vipalpanchal/Library/Developer/Xcode/DerivedData/iRealify-hkospzktmsronzeeoslnvwfniaok/Build/Intermediates/iRealify.build/Debug-iphoneos/iRealify.build/Objects-normal/armv7s/MySMSFriend.LinkFileList -dead_strip -ObjC -all_load -fobjc-link-runtime -miphoneos-version-min=4.3 -lThree20Core -lThree20Network -lThree20Style /Users/vipalpanchal/Library/Developer/Xcode/DerivedData/iRealify-hkospzktmsronzeeoslnvwfniaok/Build/Products/Debug-iphoneos/libThree20.a /Users/vipalpanchal/Library/Developer/Xcode/DerivedData/iRealify-hkospzktmsronzeeoslnvwfniaok/Build/Products/Debug-iphoneos/libThree20UI.a /Users/vipalpanchal/Library/Developer/Xcode/DerivedData/iRealify-hkospzktmsronzeeoslnvwfniaok/Build/Products/Debug-iphoneos/libThree20UICommon.a /Users/vipalpanchal/Library/Developer/Xcode/DerivedData/iRealify-hkospzktmsronzeeoslnvwfniaok/Build/Products/Debug-iphoneos/libThree20UINavigator.a -framework Foundation -framework UIKit -framework CoreGraphics -framework QuartzCore -framework AddressBook -framework AddressBookUI -lxml2 -framework AVFoundation -framework MessageUI -framework StoreKit -framework SystemConfiguration -framework CFNetwork -framework MediaPlayer -framework MessageUI -framework OpenAL -framework OpenGLES -framework QuartzCore -framework SystemConfiguration -lsqlite3 -framework AudioToolbox -framework MapKit -framework MediaPlayer -lz -framework CoreLocation -o /Users/vipalpanchal/Library/Developer/Xcode/DerivedData/iRealify-hkospzktmsronzeeoslnvwfniaok/Build/Products/Debug-iphoneos/MySMSFriend.app/MySMSFriend
ld: library not found for -lxml2
clang: error: linker command failed with exit code 1 (use -v to see invocation)