CMS Made Simple Forums

We have a big problem.
Here's the global overwiew of our site.
We already integrated about 500 pages and their is maybe 700 hundreds other page that need to be integrated.
We build a couple of modules and modify somes existing one, (we had no proplems with theses modules), not that we thing that our changes are bulletproof but their was no sign of problems with it.
We build a lot of template and css.

For now on everything was going well but suddenly as we integrated more content, we start having strange behaviour from the CMS.
The admin "pages interface" stop working. We cannot dropdown the hierarchy of content, at every click we have to refresh the page to see the result. That thing really slowdown our work.

Now templates associate to a certain section of the site won't work.

And now the worst is that we cannot submit any modifications on a page.
We try to optimize our MySQL database with all the knowledge we got with no result.

So THE BIG QUESTIONS are: is there a limit to cms made simple in teerms of quantity of pages and does anyone had used that many of ressources with that CMS

We're running on :
Linux: Redhat
Apache: 2.0.52
PHP: Version 5.0.4
MySQL - 5.0.22-standard
phpMyAdmin - 2.8.2

Thank you everyone.

Check your apache error log for error messages, I'm thinking it is probably a memory limit issue.