Problem with my game: Military units vanishing

[Comrade Lenin]

Ok, now... I've had this problem a number of times now and i'm starting to get sick of it. Sometimes i'm playing the game and, regardless of how big or small my military is, all of a sudden a couple, several, or dozens of military units will disappear at the start of one of my turns. Any kind of unit. Tanks, cavalrymen, submarines... Oh God, I got so pissed once when like 50 of my submarines suddenly vanished, along with dozens of nuclear and cruise missiles that they were carrying. I turned off the game and didn't play it again for months after that one. And I still have that problem once in a while. Once I was playing the game, and I noticed that suddenly all the other nations seemed much more aggressive to me. I wondered why, and then a few minutes later I realized that it was because my nuclear deterrent was gone! All my nuclear missiles had disappeared from their airbases, submarines, carriers, and cities! And again, it happens with ANY kind of unit. It's especially irritating when it happens while i'm in the middle of a war. Anyone else have this problem? Why does it keep happening, and what can I do about it?

Oh, and if it makes a difference, I have the Mac version of Civ 2.