You might have to find an older version of TF2, because the broken demos are on maps that Valve patched, such as Badlands and Granary and I think the difference in the maps (the version the demo recorded and the current default version) might be causing the crashes.

It's not maps alone, I tried to go through some demos for a clip, demos seem to have broken partway through. It's probably related to some specific entity. Some demos work for some time then break, others just don't load.

That's what happens to my demos as well, except for ones on custom maps like viaduct and process rc3. It might be a lucky coincidence but I'm fairly certain that demos on custom maps are fine and others aren't.

I couldn't get demos on snake, process rc3, badlands, or granary to work. I'm pretty sure that it isn't just maps that are breaking demos, as some don't break until around 80k ticks in.

A guy on Reddit sent an email to the tf team and they asked for him to submit example broken demos and the specific errors that popped up in console to help them fix it.

Send em some demos so they can fix it, cause I can't work on my project atm either. It's definitely some kind of really big error, as every single demo is broken in some way, even ones that previously worked under backwards compatibility.

Could you post the email to the guy we should send demos too, or the reddit link?

Reddit link to the thread is http://www.reddit.com/r/truetf2/comments/1i3ht7/will_the_demos_broken_by_the_most_recent_update/

The email is just the TF Team (TFTeam@valvesoftware.com)

He sent it to a specific employee he knows I think, but sending it to the TF Team works just as well.

I would take a guess at any weapon that got updated if used in a demo would cause a crash. Considering the new stats the demo would be using faulty weapons stats or knows that it would be using faulty weapon stats and thus stops loading.

apparently there was a backwards compatibility system put into place, that somehow broke this patch. Like when replaying a demo, it would only use information available at that date and time

The new demo system they made in (I THINK) late 2010 added backwards compatibility and made every demo made on the new demo system not have this problem. The backwards compatibility is so good that even if map layouts change substantially the demos still work. (even if it means players noclipping through walls or capturing control points where control points don't exist anymore) My Tangerine v Looking Handsome demo was about as broken as demos can get on the new demo system when they are working properly (my Sapper had an Engineer toolbox attached, teleporters were all upside down and diagonal, etc just model errors), and it's been through a few balance updates.

Something in the balance update broke stuff tho, coz even demos that were compatible in previous balance patches don't load. That cp_steel demo just outright crashes the client entirely now.

It's fixed now from the new update.

Let us rejoice xD