I\'m using Xcode 4 and in Build Settings all drop down lists have gone away.
Instead of the drop down lists, I have text boxes.
See this image, for example:
Some random ideas:
Try deleting / then re-set the setting.
Maybe your xcode project file .xcodeproj
is dirty.
You should give a look at its xml file > xxxxxx.xcodeproj/project.pbxproj
You did something bad to your Xcode install, reinstall/upgrade :)
Check your Xcode settings/preferences/garbage files (move / delete to reset...) which you can find there :
~/Library/Preferences/
> com.apple.Xcode.plist
& com.apple.dt.Xcode.plist
~/Library/Application\ Support/Developer/Shared/Xcode
~/Library/Application\ Support/Xcode/
~/Library/Developer/Xcode/