Add-on missing manifest.php and now can not delete in On Demand (7.6.0)

I loaded several third party add-ons in Module loader to evaluate that would help me setting up workflows in On Demand Professional 7.6.0. Now that I have chosen the right method of customization, I would like to remove the other add-ons as I worry they may causes problems with one another. However, when I go to Disable or Uninstall these add-ons, I get an error that manifest.php is missing. This happens with both add-ons I am trying to uninstall.