Can't Enable IMAP

Can't Enable IMAP

I cannot enable IMAP on new emails accounts. After activating IMAP and getting the success confirmation message, I refresh the page and it appears again NOT ACTIVE.

This is for mipedido@epet.cl and no-responder@epet.cl. This last account the IMAP was enabled and I deactivated it to test, now I can't enable the IMAP again.

Help!