You have to install latest iOS version (5.1) to your xcode to detect your ios5.1 devices. But it does not included in xcode4.2 installer, so you have to upgrade your OS to 10.7.

There is a way to install iOS sdk 5.1 to your xcode 4.2 running on Mac OS X 10.6.x.

First, you have to download latest xcode installer here (mine is xcode_4.3.1_for_lion.dmg, you may have to login to download)

Open terminal (Application->Utilities->Termial) and type these commands:

sudo cp -R /Volumes/Xcode/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS5.1.sdk /Developer/Platforms/iPhoneOS.platform/Developer/SDKs/
sudo cp -R /Volumes/Xcode/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator5.1.sdk /Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/
sudo cp -R /Volumes/Xcode/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/DeviceSupport/5.1\ \(9B176\) /Developer/Platforms/iPhoneOS.platform/DeviceSupport/
sudo rm -f /Developer/Platforms/iPhoneOS.platform/DeviceSupport/Latest
cd /Developer/Platforms/iPhoneOS.platform/DeviceSupport/
sudo ln -s ./5.1\ \(9B176\) ./Latest

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Restart you xcode and now it works.

This project aims to duplicate the methods present on Mac OSX which allow creation of NSAttributedString from HTML code on iOS. This is useful for drawing simple rich text like any HTML document without having to use a UIWebView. (Previously known as "NSAttributedString Additions for HTML")

GitHub