Some of the Drupal Admin pages did not work.
For example the menu: Home »Administer» Site Construction »Menus» Navigation
The problem seemed to be solved after disabling the various modules. But when I went looking for the module what causes the trouble, it was a bit random. In short, the problem was not in the modules, but the extra memory usage that the modules used.
The status reporting in Drupal menu Home »Administer» Reports »Status report, was the PHP memory limit to 16MB and it was ok.
Yet I tried to raise the limit to 32MB of PHP and it appeared to work. One way to increase the PHP memory limit is in the file** ./sites/default/settings.php**
Put the following line, under the heading PHP settings:
ini_set ( 'memory_limit & #_39;, '32M ');
It is also possible to increase the amount of php memory via the .htaccess file. Just add the following line to .htaccess:
php_value memory_limit 32M