cPanel update to breaks RoundCube

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http://forums.cpanel.net – After the latest cPanel update three hours ago from to RoundCube stopped working. After the webmail RoundCube log in I get: Quote: SERVICE CURRENTLY NOT AVAILABLE! Error No. [501] Which looks like a 501 internal server error (permissions?) ... I did a forced cPanel update (/scripts/upcp --force), but that did not change anything. Horde and Squirrel are working fine. Any help? (HowTos)