It usually means that your data files were not updated/installed correctly, possibly because a file was locked by the OS.
Are you playing Express or the full version?
If it's Express, you should try re-installing.
If you're playing the full version, try rebooting. If that doesn't fix the problem, you can edit the registry to force Impulse to re-download the update.
In XP, go to Start->Run and type regedit. In Vista, type regedit in the search box.
The registry key is located under HKEY_LOCAL_MACHINE Software\Stardock\Drengin.net\PolMachine08 and just change the value of version to 1.49.