We're running Joomla 3.6.2 and CiviCRM 4.7.11, however we recently made some adjustments that prompted us to uninstall the Summary Fields extension. Essentially, it was installed in a different directory than the default settings. We reset the paths and that cause problems. So, we uninstalled and reinstalled, so extensions are now in the default directory. The problem is that when we configure summary fields and set it to update "when the form" is submitted, we receive the error "Error adding custom field 'contribution_amount_last': DB Error: already exists" (same error for other fields as well, like "last donated", etc.). Is there a way to do a complete uninstall of this, or is there a better way to handle this error?
We ended up disabling the extension via phpmyadmin, which enabled the "uninstall" link in the UI. Un-installation went fine, and we did a fresh install and now everything appears to be working fine.