Access to Customer interface

[snrt]

Hello
I'm starting to OTRS, I created two users: one operator OP1 and USER1 client.
I can access the OTRS operator interface, unfortunately I can not access the OTRS Customer interface, I get the following message: "Login failed Your username or password was Entered Incorrectly!." Yet I have checked the login and password.
Should I set something in the "system configuration" of the Administrator Menu.
Thank you