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I've found a partial solution: I do not have a fully functional robot yet - I was assuming I could just set up slam_gmapping with a Hokuyo URG-04LX laser ranger and an ASUS EeeBox running ROS. That means I had not set up my /tf or /odom nodes. I'm not sure why this caused trouble, but apparently it did. As a temporary fix, I used this launch file to initialize the laser before I ran through the steps in slam_gmapping tutorial:

 <launch>
    <node pkg="hokuyo_node" type="hokuyo_node" name="scan">
    <param name="port" value = "/dev/robot/laser" />
    <param name="max_ang_degrees" value="90" />
    <param name="min_ang_degrees" value="-90" />
    <param name="frame_id" value="base_scan" />
    </node>

    <node pkg="tf" type="static_transform_publisher" name="hokuyo_static_tf_publisher" args="0 0 0 0 0 0 1 base_link base_scan 50" />

    <node pkg="tf" type="static_transform_publisher" name="odom_static_tf_publisher" args="0 0 0 0 0 0 1 odom base_link 50"/>

</launch>

All I did in this file was set up a static identity transform from base_link to base_scan, and from odom to base_link. The dual 32-bit error did not appear, thankfully, but another problem did happen: In the terminal running slam_gmapping, this warning appeared when I played back the bag file:

[WARN] [1312405487.766138148]: TF_OLD_DATA ignoring data from the past for frame /odom at time 1.31241e+09 according to authority /play_1312405475737786833
Possible reasons are listed at 
[ WARN] [1312405487.768969562]: TF_OLD_DATA ignoring data from the past for frame /base_scan at time 1.31241e+09 according to authority /play_1312405475737786833
Possible reasons are listed at 
[ WARN] [1312405487.780878676]: TF_OLD_DATA ignoring data from the past for frame /odom at time 1.31241e+09 according to authority /play_1312405475737786833
Possible reasons are listed at

and then nothing, so I don't know where 'Possible reasons' are listed. After that, when I ran the map_saver function, it began but I received a 'Waiting for map' message that did not end until I canceled the process.

There must be something else that's obvious, I'm just missing it. Can anyone spot it?

Thanks,

Khiya