PHP 7

[langi]

Hello

I set up with roundcube (latest version 1.2) a webmail software that works well. Now I wanted to switch to PHP 7 (roundcube should be compatible).
Once PHP 7 is activated, appears in completing the destination address respectively the following error message:

An error has occurred. Server error (forbidden).
The error log the following message appears:
"PHP Error: Request security check failed (POST /mail/?_task=mail&_action=autocomplete)"

What's the problem?
Thank you for your support.

Regards
Langi