This problem has been frustrating me ever since I first got PTW.
If I play on a map or scenario, I start the game fine, after a while (say up to the year 1000AD), I stop the game, save it and log off for the day, when I load it, I get a Data IO error: CTZN at the 38% mark.
This problem has also now affected CIV3 too!

I have used all the latest patches, (1.29 and 1.21) but nothing works. HELP, I'm going out of my mind, and I'm close to getting rid of the games!

Try unistalling and reinstalling civ3 and ptw, and keep the save in and other folder, see if it works then