After upgrading to Drupal 4.7.4 server stopped responding

After upgrading to Drupal 4.7.4 (no problems) and running update.php (no errors) yesterday, a few hours later Drupal stopped respondig completely; I have no idea, if this is really correlated to the upgrade, or was just a pure coincidence. Drupal is hosted on a dedicated server which is accessible through SSH as usual; the installation is about 14 months old (starting with Drupal 4.6) and never died completely before. By "died completely" I mean: Opening a random page administered by Drupal resulted in the browser wainting for hours (!) without showing anything, neither the page's content nor an error message.

* System: Apache 2, Debian GNU/Linux "Sarge", kernel 2.4.29 (SMP); dedicated server, Celeron CPU, 2,4 GHz, 512 MB RAM; other notable software running: phpMyAdmin, Gallery2, MediaWiki, Postfix. PHP should be version 4:4.3.10-16, MySQL is 4.0.24-10-sarge2, Apache2 is 2.0.54-5sarge1.

* Postfix works fine; phpMyAdmin, G2 and MediaWiki deliver pages (so MySQL and PHP are working), but seem to be unusual slow (Drupal is always slow compared to those); static pages are delivered by Apache2 pretty quickly.

* Logs: Nothing unusal in /var/log/syslog and /var/log/messages.

/var/log/apache2/error.log:

[error] an unknown filter was not added: INCLUDES (no idea what this might be)

Approaches to open Drupal URLs don't show up in /var/log/apache2/access.log.

* Ran a check für all 145 tables in database 'Drupal' via phpMyAdmin, resulted without exception with "status OK".

* Moved all (!) 3rd party modules out of ../modules, Druapl started to deliver the (home-) page again; lots of error messages like in_array(): Wrong datatype for second argument... in /portal/admin/logs. Deactivated all possible modules in /admin/modules, freed about 80 MB of RAM (!). but resulted in lots of new error messages, e.g. Duplicate entry 'modules/legacy.module' for key 1 query: UPDATE system SET description = 'Stellt Funktionen zur Kompatibilität mit älteren Drupal-Versionen zur Verfügung.', name = 'legacy', bootstrap = 0, filename = 'modules/legacy.module' WHERE filename = 'modules/modules/legacy.module' in /var/www/portal/includes/database.mysql.inc in Zeile 121.. Started to activate the default modules one by one; Drupal delivered still pages pretty quickly.

* Started to move 3rd party modules back; activating them one by one, Drupal became increasingly slow again (~ 20-30 seconds per page), and the protocol filled again with the mentioned cryptic errors like Duplicate entry 'modules/legacy.module' for key 1 query: UPDATE system SET description = 'Stellt Funktionen zur Kompatibilität mit älteren Drupal-Versionen zur Verfügung.', name = 'legacy', bootstrap = 0, filename = 'modules/legacy.module' WHERE filename = 'modules/modules/legacy.module' in /var/www/portal/includes/database.mysql.inc in Zeile 121., and in_array(): Wrong datatype for second argument in /var/www/portal/modules/forum.module in Zeile 710.

* During reactivating the module 'nodewords', Drupal died again. Moved 'nodewords' out of ../modules, and Drupal started responding again. Changes in /admin/settings etc. took > 30 seconds per page at this moment. I suspect a possible incompatibility between the module 'nodewords' and Drupal 4.7.4; I find this notable since the module worked fine under Drupal 4.7.3; however, this can be merely a coincidence. If not, othe modules might be affected by this as well. Also, I don't understand why this happened not immediately after the upgrade but with a delay of several hours (caching?)

At the moment Drupal seems to work as usaul (pretty slow, but delivering pages).

If this problem applies only to the module 'nodeweords', please ignore the description and close the issue.