[ros-users] tf and time tutorial

in the tf and time tutorial there is a line
now = rospy.Time.now()

but it crashes every time I run it.
the error is
[listener-5] process has died [pid 6449, exit code 1].
log files:
/home/ringo/.ros/log/df877bf2-910c-11e0-bc06-080027911c3f/listener-5*.log


now = rospy.get_rostime()
crashes as well


now = rospy.Time(0)
works ok.

am I missing something?
Ringo