You need to split the setRPY call and the multiplication into two different statements. At the moment the last line of your code is trying to multiply m a tf::Matrix3x3 by the returned value of the setRPY() method. This is a void function so you code is trying to do tf::Matrix3x3 * void hence your problem. Try the following code instead:
tf::Quaternion q( four_result_pose.orientation.x,  four_result_pose.orientation.y,  four_result_pose.orientation.z, four_result_pose.orientation.w);