PCL Header timestamp

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The pcl_ros tutorial example doesn't work:

#include <ros/ros.h>
#include <pcl_ros/point_cloud.h>
#include <pcl/point_types.h>

typedef pcl::PointCloud<pcl::PointXYZ> PointCloud;

int main(int argc, char** argv)
{
    ros::init (argc, argv, "pub_pcl");
    ros::NodeHandle nh;
    ros::Publisher pub = nh.advertise<PointCloud> ("points2", 1);

    PointCloud::Ptr msg (new PointCloud);
    msg->header.frame_id = "some_tf_frame";
    msg->height = msg->width = 1;
    msg->points.push_back (pcl::PointXYZ(1.0, 2.0, 3.0));

    ros::Rate loop_rate(4);
    while (nh.ok())
    {
        msg->header.stamp = ros::Time::now ();
        pub.publish (msg);
        ros::spinOnce ();
        loop_rate.sleep ();
   } 
}

The compiler complains with the following:

error: no se puede convertir ‘ros::Time’ a ‘uint64_t {aka long unsigned int}’ en la asignación (it's in Spanish, I don't know how to change my compiler language)

which is something like:

error: 'ros::Time' cannot be converted to 'uint64_t {aka long unsigned int}' in assignment

Has somebody else faced this problem? I am running ROS Hydro, on Ubuntu 12.04.

Thanks