Folks,
It was NEVER a good idea to rename a campaign mod folder from one of the original four (like americans or teutonic) in order to make a mod work. That was always just a quick fix. The proper way to do it was to use the launcher replacement that made the regedit entries or to learn how to edit the registry. Now it's coming back to haunt you.
You can have an unlimited number of mods if you properly install MTW2 Kingdoms and go around it, not renaming folders. At least that's how it used to be.
The Steam update has always been a mixed bag. I've personally seen it corrupt files, and it's a real pain in the ass when you're modding and done work for a month and you lose everything. Now's a good time for any modder to save their work and NOT do the update until we know what's what. Personally I'm not even booting into MTW2 Steam until things get settled down from this debacle. RTW1 works just fine and is NOT a Steam product on my computer...and for good reason.
For years folks have had Steam related modding issues, all of which several of us worked on solving tirelessly, answering questions patiently, and gritting our teeth for the next one. Honestly, this is why the regular versions of CA's games are much better EXCEPT it's certainly true that DVDs can go bad by being scratched. I've had this happen myself.
Follow irishron's updates and anyone else who's working on it. Give him rep or anyone who finds solutions. Don't ask the same question only slightly worded differently. Hopefully this will get worked out by Steam, CA, and some community members in the interim.
Steam has a very bad habit of downloading but then if you do a verify, you'll see errors. Make sure you understand how to check this too. Sometimes it takes numerous times to get it completely updated without errors. Because some people used the folder rename shortcut, it's possible you've lost your savegames, will almost certainly have to reinstall mods, and so you can bellyache about it, but what's to be done?

happens and rolls downhill.