Well,... Here is the answer to backing up this site.
ProBoards specifically creates backups of forums hosted by them, for emergency related purposes, where a backup must be used in cases where something happens, and a backup is the only way to recover the forum.
Per the terms of service, users allow for their content to be used by ProBoards to be posted on ProBoards forums. Period. Any attempt to harvest the content is a violation of the terms of service as well as a violation of the rights of those who posted on your forum.
Bottom line is that you do not own the content on the forum and therefore are not entitled to it.
Quote from ProBoards Admin
Michael Stone
ProBoards Admin
Support Manager
Using a program to scrape data off of a forum is not allowed per the TOS.
(TOS is an acronym for Terms of Service)
We have provided a way for you to download and retain your own data from the forum, the data of other users does not belong to you.
You are only permitted to backup your own posts on the forum, as each user owns the material they have posted.
You can download your posts from Account Settings and clicking on Export Member Data.
End quote.