New Custom Field

I purchased this plug-in, but the wizard to create the custom field does not work.
When I click on the “Create new custom field” button a dark background appears and hangs with with this level opening with js event “<div class =” modal-backdrop fade in “> </ div>”. Forcing the elimination of the ?backdrop? class, even when I click on the “Open Custom FieldWizard” button, I see a dark background, despite a long wait. Can you help me to fix this problem? Thanks.