login error 404 when opening Marketo Designer (Landing Pages and emails)

Hello,

All of a sudden, I cannot open Marketo Designer to create or visualize Landing Pages and Emails: when I try to do that, I am redirected to a login page and although I fill the correct login information, I keep getting a "login failed error (404)". Anyone has already stumbled upon a similar issue and can help me?

Obs.: The login problem only occur when I try to open de designer: I can access any other area of Marketo normally.

Thanks in advance!!