We've managed to reproduce the issue that was causing some savegames to not load properly; 0.26.0d should fix it for good.
For those who are curious *why* this was happening; in the rest version we added achievements. Unfortunately that added some additional data fields for tracking stuff in the system save file, and some older savegames struggled with that.
It should be all fixed now, and there should be no problems using your existing saves. Thanks to all the people giving us feedback, sharing their log files and testing stuff for us.