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The difference between "map->odom" and "odom->map" is who is the parent and who the child in the tf tree.

In the example code that you posted you're publishing base_link as parent of base_laser and odom, and then map as parent of odom. Map and base_link cannot both be parents of odom. The error that you reported usually happens when two parents of the same node are being published, resulting is an unconnected tree. I suggest you to visualize your tf tree using "rosrun tf view_frames" as Eric says.

It could be helpful to know which nodes are you running, because other nodes could be broadcasting tf transforms.