no problem. When I added the [bbp-forum-index} and [bbp-topic-index] to my forum page I added a header before the shortcodes. This made the breadcrumbs go awry and I think that’s why it could not naviagte back to the forum page and got a 404 error instead. I deleted the headers and was then able to create topics and replies with no problem.
I have also found a really useful post to remove the sidebars on the forum page but will post this in a new topic to avoid confusion.
I have had a lot of problems with bbpress and Canvas and am waiting a response on a bbpress search plugin that just searches the forums. I shall post the resolution on that one when it comes.