warning 'Invalid argument supplied for foreach()' at /wp-admin/includes/class-wp-list-table.php 344:

[Scott S]

The problem only appears on the "Must Use" and "Drop ins" tables in the plugins page, does not effect normal plugins view, and doesn't seem to affect mu/drop-in functionality

Only happens on 3.5.1

Tried on 6 different 3.5.1 installs, all show the same error

Debug trace results:

Backtrace from warning 'Invalid argument supplied for foreach()' at /opt/lampp/htdocs/themedev/wp-admin/includes/class-wp-list-table.php 344:

1. /opt/lampp/htdocs/themedev/wp-admin/includes/class-wp-plugins-list-table.php 400 calling row_actions()
2. /opt/lampp/htdocs/themedev/wp-admin/includes/class-wp-plugins-list-table.php 296 calling single_row()
3. /opt/lampp/htdocs/themedev/wp-admin/includes/class-wp-list-table.php 796 calling display_rows()
4. /opt/lampp/htdocs/themedev/wp-admin/includes/class-wp-list-table.php 736 calling display_rows_or_placeholder()
5. /opt/lampp/htdocs/themedev/wp-admin/plugins.php 431 calling display()

Could not reproduce on a clean install neither in 3.5.1 nor in 3.6-alpha.

Do you have a plugin that hooks into plugin_action_links filter? Looks like the only way to get this warning is to hook into that filter and return something other than an array:
​http://core.trac.wordpress.org/browser/tags/3.5.1/wp-admin/includes/class-wp-plugins-list-table.php#L364

Ah yes, it would seem my co-admin updated some plug-ins shortly after I updated the WP install - the issue is being caused by ​http://wordpress.org/extend/plugins/wp-editor/ this plugin. I'll notify the author.

That'll teach me to check the logs prior to reporting a bug!