Hi,
Maybe this can help cause I think you are overwriting classes :
import gs.*;
import gs.plugins.*;
import gs.easing.*;
import com.greensock.*;
import com.greensock.easing.*;
Try to change the lines of code above and import only:
import com.greensock.*;
import com.greensock.easing.*;
I had the same error and was for this cause.
I hope you can understand, my English is not very good