Enable remember me in Legacy and Symfony, according to what is explained in EZP-24367 and apply the patch provided in that Jira Issue.

Open the backoffice, edit any content and try to preview it.

You will get the following error in the preview:

*The requested page could not be displayed. (20)*

The requested address or module could not be found.
Possible reasons:
The address was misspelled. Try changing the URL.
The name of the module was misspelled. Try changing the URL.
There is no <login> module available on this site.
The site is using URL matching to determine which siteaccess to use, but the name of the siteaccess is missing from the URL. Try to add the name of the siteaccess; it should be specified before the name of the module.

The log file will display:

[ Jun 02 2015 11:45:04 ] [192.168.56.1] index:
Undefined module: login
[ Jun 02 2015 11:45:04 ] [192.168.56.1] error/view.php:
Error ocurred using URI: /cpanel/login