You have to set your project to compile with the Glass GDK.
Make sure you're targeting 15, have the GDK downloaded as per the other answer, and then:
Select your project on the left side of the screen, open project poperties (alt-enter, or right click -> properties), go to Android tab, scroll down to Android 4.0.3, and in that section will be the Glass Development Kit Sneak Peak. Check the box next to this, hit ok and everything should start working.
EDIT:
Just to make sure, your manifest should have this line:
<uses-sdk
android:minSdkVersion="15"
android:targetSdkVersion="15" />