Error loading/installing iOS 5.0 Simulator in XCode 4.4.1

I'm new to iOS and Apple.

Just got XCode installed, but when I try to dowload/install iOS 5.0 Simulator using the 'Download' tab of XCode preferences, I get the following error consistently:

Failed to mount file://localhost/Users/reza/Library/Caches/com.apple.dt.Xcode/Downloads/Xcode.S DK.iPhoneSimulator.5.0-5.0.0.1.dmg at file://localhost/var/folders/bm/kz0d00lx18ncwq3fxyf50pn00000gn/T/attached-image -122057767f890c101413b3e8c64917b42f1eb792/: not recognized

What I'm doing wrong and how can I fix it, Please ?

I'm using Xcode 4.4.1 on OS X 10.8.1