Does the game crash (exception error) or does the unit select freeze happen, where the game will still appear to be functioning but units won't take orders and nothing will build properly? If the former, make sure you have this:
http://thrawnsrevenge.com/forums/index.php?topic=4976.0
If the latter, use this:
http://www.moddb.com/mods/thrawns-revenge/downloads/unit-selection-freeze-fixer-utility-v2
Also, if it's the latter you would do me a great favor if you tried this tool instead of the one Corey linked:
http://thrawnsrevenge.com/forums/index.php?topic=5610.0Backup your save games before you use it!
Basically this is a mod launcher that is supposed to do the exact same thing as the tool that Corey linked to.
How to use:
1. Launch your game with the launcher.
2. Load your corrupt save game and just overwrite it, the launcher will then detect that a save game has been changed.
3. Quit the game, the launcher should then ask you if you want to use the Defreezer. Click yes and select the corrupted save game and then click defreeze.
Of course all of this only works if this is the unit selection bug Corey mentioned.