[ros-users] Map creation hangs

Hi,
I am executing a tutorial "How to build a Map using Logged Data". Till step
6 everything works fine but at step 7 while saving map map.pgm the process
gets hanged.
It shows
rootx@rootx-laptop:~$ rosrun map_server map_saver map:=dynamic_map
[ INFO] 1275144978.345087000: Waiting for the map
For long period of time.
I have downloaded a bag file from the server.
Please help!
-Prasad