problems with the Envayasms - master downloaded from Github

[Nels]

Hi everyone.

I am trying to build the Envayasms - master downloaded from Github on NetBeans, and I have fixed most of the errors which I resolved by adding the required JAR files.
But there is one stubborn error which I am finding hard to fix:

code snippet:
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.os.Bundle;
import android.preference.Preference;
import android.preference.PreferenceActivity;
import android.preference.PreferenceScreen;
import android.view.Menu;
import org.envaya.sms.App;
import org.envaya.sms.R;

The last line, is giving me problems, the R class is underlined and can not be found, I have attempted many solutions which proved to be futile. Please help.

Thank you :-).