QuickTime Player has stopped working

I have produced a ton of videos on Mac, that I am distributing to my bosses who own Windoze PCs, mostly over the internet. I normally don't do Windows. I have made sure the latest Quicktime is (according to what the function says) installed on their computers.

While I believe I've produced all these videos with the same H.264 codec (many in the same session, reprocessed ProRes through Quicktime 7 Pro), only about a third of them play (on Windows) the first time (on Mac I've never seen a problem). Some of them will play after a long delay (maybe slow internet, but the same file comes up in seconds on my Mac, on the same internet connection across the room). The majority of those files won't play at all, instead getting the "

QuickTime Player has stopped working"message, over and over.

I've read some archived posts that mention other people having the same issue . . . with no definitive resolution, just probing around different menus in the PC. The PC's I'm working with don't even seem to have the same tabs and controls mentioned in those articles. So here we sit with what should be a simple basic function, of playing a quicktime file made on a Mac, and showing it on a quicktime installed PC. And it doesn't work.