One of our templates requires the word 'update' in the text copy, but whenever we edit it to add the word, on save we get "Error. The page you requested was not found."
The same error happens when the word is joined to another, for instance 'updatefor'.
We have tested and get the same error regardless of whether the word is added as text copy or even a class name.
The same error is not found when we edit page or channel content with the same word.