PDOException error - Google AdWords Conversion module
OK I would take this approach. First off you need to look at the system table within your Drupal DB. Since you can't for whatever reason disable the module from the UI you'll need to disable it from here. You can do this by navigating to the row representing the module, and setting the status column to 0. Once you've done this clear your cache.

The error message you're getting is due to a database schema inconsistancy, so what I would try do is navigate to the Modules -> Uninstall (/admin/modules/uninstall) and see if I can now uninstall the module. Depending on how the module is written, this should invoke hook_uninstall and undo any database scheme alterations made when the module was initially installed.

Hopefully this will get rid of the nasty PDOException you're running into when editing your webform.