[Plugin: WP Super Cache and also Simple Press] PLEASE help,Cannot make this work

It is impossible for anyone to register on two of my sites (password never shows up), and I’ve spent untold hours trying to figure this out. I’ve tried everything else, and I followed a lead that it’s at least possible that the caching in relation to Simple Press could be the problem. (SP is on both of the sites with the problems.)

Here’s what I’m getting:

WP Super Cache is not properly configured to work with Simple:Press. Please visit your WP Super Cache settings page and in the accepted filenames & rejected URIs section for the pages not to be cached input field, add the following string:

/forum/

Then, please clear your WP Super Cache cache to remove any cached Simple:Press pages

Going to WP Super Cache Settings brings up this message:
Permlink Structure Error
A custom url or permalink structure is required for this plugin to work correctly. Please go to the Permalinks Options Page to configure your permalinks.

I have NO@!!!!!!!!!!!!!!!!!! idea what the permalink settings should be here. I am having to run three sites because NOBODY who has techie experience/knowledge will step up to the plate (and there are a lot of people in the site community in this category!! They’re happy to use the site, but helping… forget about it.) All for free… all a labor of love… I am at the end of my rope with this and there is no end to it.

I’m trying to just take this one step at a time and not have a nervous breakdown… does anyone know anything about what the permalink settings “should” be in this case? I can’t get any further at all until I know this.

Exhausted,frustrated, ready to smash all computers and write everything in a notebook with a pen from now on…

Anise
P.S.: The site where this error is coming up is at:
https://www.allfics.com