OK, I'm stumped.
I couldn't get into simple press forum randomly. I troubleshot the hell out of the plugin. Turns out its not the plugin.
The forum sets itself up on a page. I wanted a wider content area, so I made a page template. It's the page template that won't work. ANY page template won't work. I went so far as to make an exact copy of page.php and drop the proper header in there. No dice.
When I set up a new page, I get my page templates listed in the dropdown as they should. But when I visit any page with a template applied, I get a 'IE cannot display this webpage' page. Not even my 404 page in my theme (which works, tested). Switch back to default template, all is well.
Any ideas what would cause that? I mean, it's nothing to do with template coding obviously, as my perfectly functioning page.php does not function as a template.
Problem occurs with plugins all deactivated too. The template had worked just fine about a week ago or so.... it just quit. All standard wordpress templates work. index, page, single, 404, etc....