When a form is deleted in the backend control panel, the forms associated entries in jos_chrono_contact_emails are not removed. The delete needs to be cascaded to the other tables.
Thanks for the report, I will fix this!🙂
Max, ChronoForms developer
ChronoMyAdmin: Database administration within Joomla, no phpMyAdmin needed.
ChronoMails simplifies Joomla email: newsletters, logging, and custom templates.