This just happend to me a minute ago, but after researching a while, and read this post I notice this.
There is a custom R class with you app name, so when you try to import the missing class (in Eclipse, press Ctrl + Shift + O to import missing classes (Cmd + Shift + O on Mac)), you should see two posible classes the normal:
import android.R;
And a custom class with your project namespace:
import com.yourname.yourapp.R;
If you choose the custom class, problem solved!