Building map (map_saver) not working with user-made bag files

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I am following the tutorial on the ROS wiki on how to create a map from bag files( http://wiki.ros.org/slam_gmapping/Tut...). Whenever I follow the steps on a downloaded bag file (they give you a ready made bag file to download on that page) it works fine. However, when I try it on the bag file I made, it doesn't work (just says waiting for map and never does anything). I already opened the bag file I made in rviz and it works great, I don't understand why using this bag file makes it not work.