Android requires compiler compliance level 5.0. Please fix project properties

Today, I moved a different work space from my old work space, but I imported some of the projects from my previous project and I started to get this error out of no where. I figure out it's something to do with the Eclipse compiler issue. To fix this you need to change globe flag which is located here

Window - > Preferences -> Java -> Compiler - > Change JDK compiler complience level to 1.5 or greater. (I use 1.6)