getting the same error here -- along with this one when TF shuts down.
https://support.steampowered.com/kb_art ... -UOHK-5653
some of the items in this article, like running sfc.exe, would not be my preferred first action in trying to troubleshoot this one.
EDIT: ok. sat down this afternoon and worked on this. quite a bit of reading of the steampowered.com forums (bleh, some people should never post to forums).
* deleted all old map files (~5GB)
* deleted and redownloaded game content
* deleted
${steam_install_path}\steamapps\z0th\team fortress 2\tf\particles directory
* defragmented game files
im pretty sure it was one of the last two that got things working again.