I don't know much about TF2... might have to wait until I update this plugin to work with defined database and not clientprefs... The reason the players are getting that error is because the AreClientCookiesCached is still false:
* Checks if a clients cookies have been loaded from the database.
* @param client Client index.
* @return True if loaded, false otherwise.
* @error Invalid client index.
^^ That's the one I'm using. And there's a repeating 10 second timer to check if client cookies are cached and once they are, the client is allowed to use sprays or not (banned).