Hofmockel.org

Symptoms - After adding a new module the administer -> module
link fail (link is dead). When the module directory is removed the link
returns.

Solution - This is most likely a memory issue. PHP default load sets
"memory_limit = 8M" in /etc/php.ini. The more modules you add the more
memory you will need to run the module script. Change memory_limit to
20M. Requires a restart of httpd.

Ref:http://drupal.org/node/13358