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Deleting the module folder outright, without uninstalling it through the UI/Drush (even manually in the DB) is bound to cause a few problems.

To get rid of any errors caused by Drupal thinking the module files are still there, you can simply delete the row in the system table which corresponds to the relevant module; but make a database backup first, of course.

In case you haven't come across the pages before, you can disable modules at http://mysite.com/admin/modules and uninstall them at http://mysite.com/admin/modules/uninstall through the UI, or use Drush.