All what I did new is to instal Email Users plugin yesterday. I don’t know if that could do it. I deleted it now, but Forum is still down. 

so go to forum – integration – page and permalink…  make sure the correct wp page for the forum is selected…  try updating the permalink…

Permalink update worked! Thanks! Do you know what could happen? 

It is possible that the new plugin scrambled the WordPress rewrite rules which the forum needs to display itself. Or maybe something else did.

I did it again. It wend down for no reason and after updating permalink it is back up. 

perhaps try the tweak here:  https://simple-press.com/support-forum/sp5-general-topics/404-errors-1/page-2/#p124646

I also just noticed that that all other static pages going down too and they are back up after updating permalinks. (home page and buddy press pages are fine). 

so resolved?

No, it goes back down every day and I have to update permalinks to get it back up. 

Mr Papa said
perhaps try the tweak here:  https://simple-press.com/support-forum/sp5-general-topics/404-errors-1/page-2/#p124646

Do you want me to do this? 

go to simple-press/sp-startup/sp-load-site.php and find this line of code:

add_action(‘template_redirect’, ‘sp_404’);

and either comment it out (put # before it) or just remove it…

certainly worth a try… mixed results for the handful of folks with this issue… I can give you something else to try if that does not work… something is messing with wp permalinks…