I was tryign to replicate some of the problems reported and uninstalled and removed all the modules.
Upon removing the last module the warning
Warning: Invalid argument supplied for foreach() in /srv/www/htdocs/admin/page.modules.php on line 230
Warning: Invalid argument supplied for foreach() in /srv/www/htdocs/admin/page.modules.php on line 157
is shown.
Clicking on Setup gives the following warnings
Warning: array_keys() [function.array-keys]: The first argument should be an array in /srv/www/htdocs/admin/functions.inc.php on line 289
Warning: Invalid argument supplied for foreach() in /srv/www/htdocs/admin/functions.inc.php on line 289
Going back into Tools gives the same warnings as above.
Clicking on Online Modules gives
Warning: array_key_exists() [function.array-key-exists]: The second argument should be either an array or an object in /srv/www/htdocs/admin/page.modules.php on line 122
22 times.
Once you have downloaded a module you still get the warning
Warning: array_keys() [function.array-keys]: The first argument should be an array in /srv/www/htdocs/admin/functions.inc.php on line 289
Warning: Invalid argument supplied for foreach() in /srv/www/htdocs/admin/functions.inc.php on line 289
but this goes should you reload the page or click on something else.