Trying to change pop account to imap account.

pop account exists in zd. i get the above error when i try to add the imap account (same email address as pop).

my goal is to move from pop to imap with the same email address. i don't want to delete the pop account unless i know everything will come back, i.e. from export file. so i'm trying to hold on to old pop while moving to imap to ensure nothing is lost.