Well, I am sorry to say that I experienced this bug with the *patched* version, with two savegames that were saved with this same version. This is what happens:
Load 'slot3'
...subsystem 'base' - loaded 23056 bytes
Initializing aircraft and aircraft-items ...
...aircraft and aircraft-items inited
Cmd_AddCommand: popup_aircraft_action_click already defined
Cmd_AddCommand: ships_click already defined
Cmd_AddCommand: ships_rclick already defined
Cmd_AddCommand: multi_select_click already defined
Activate stage intro
...subsystem 'campaign' - loaded 269 bytes
...subsystem 'hospital' - loaded 2 bytes
...subsystem 'market' - loaded 2176 bytes
...subsystem 'research' - loaded 6288 bytes
...subsystem 'employee' - loaded 4945 bytes
...subsystem 'aliencont' - loaded 0 bytes
...subsystem 'production' - loaded 22 bytes
...subsystem 'aircraft' - loaded 1 bytes
...subsystem 'messagesystem' - loaded 6836 bytes
...subsystem 'messagesystem' could not be loaded correctly - savegame might be broken (3e)
Changing to Singleplayer
I don't know how to reproduce it, though. I have previously left the game a dozen times and loaded the two savegames with no problems. I also tried to start a new campaign, play a little, save now and then, leaving the game, and trying to load it again and it worked. So it may need a special trigger that I don't know.
BTW, I still have two other savegames that are from 2.1.1 beta, and they show the exact same message. So, this might be some leftover from the 2.1.1beta code that makes the game be saved incorrectly or with old-style data.
I am using 2.1.1 (the latest installer; I got the patch and saw that the "ufo" executable was the same as this one) on Ubuntu Feisty Fawn (7.04).