Username and password are specified while installing Afterlogic. If you do not know your username and password, you may find them in the file data/settings/settings.xml (default location path is /usr/local/mgr5/www/webmail-afterlogic/webmail/data/settings/settings.xml) (in some versions in adminpanel.xml).
Directories
<AdminLogin>admin</AdminLogin>
<AdminPassword>password</AdminPassword>
By default ISPmanager installs Afterlogic into the directory /usr/local/mgr5/www/webmail-afterlogic/webmail/
Afterlogic uses Dovecot for authorization.
In case of the error, The username or password you entered is incorrect. make sure that Dovecot is up and running.