That appears to be 2 folders named Warnings.
1) Get the user ID of the account in question.
su - zimbra
zmprov ga <account>@domain.com zimbraId
1) Login to mysql on the zimbra host
mysql
2) Change to zimbra database
use zimbra;
3) Find the group ID for the account
select group_id from mailbox where account_id="<zimbraId>";
4) Change to the mboxgroup<group_id> database;
use mboxgroup<group_id>;
4) Find the duplicate entries
select * from mail_item where name="Warnings";
Post us the output from that - or if you know what you're doing you might proceed to:
5) Change one of the duplicate folder names
update mail_item set name="<new name>", subject="<new name>" where id=<id number>;