Devel.module is a help for developers. I'm sure that it is really great for most people, but I had a Devel.module fatal crash which left things very dead. I can’t solve it but this is how to get your site back
On the advice of the great book Pro Drupal Development by John VanDyk and Matt Westgate, I installed the devel.module to provide diagnostics. At first, with nothing enabled, the "devel" menu options and config appeared, and no harm was done. As soon as I enabled some options, I was locked out of the whole site. Every page produced a fatal error message from Apache. This meant that I could not simply back out by uninstalling the module – because I could not get to the admin screen. In short, something of a disaster. If you are in this pickle, read on.
I removed the devel folder from modules. Next went through the database with my old friend Navicat (but phpMyAdmin would suffice), and removed the devel_* tables. There were also some core tables which had lines with "devel"-related info. To find those, I sorted the tables by date so I could concentrate on the most recently-used tables. Then it was just legwork.
But (you knew there had to be a "but")… the site didn’t come back despite removing every reference to devel. The last step which thankfully made the difference, was to run the url at <mysite>/cron.php . This still provoked an Apache error, but then going to the normal site pages worked OK. Hurrah.
This was all for Drupal v5.