PHP error in Roundcube LDAP lookup

[dsp3]

In roundcube, when I begin to type in an email address I get a popup 
with:
"Server Error! (Internal Server Error)"
Auto complete fails.

In /var/log/roundcubemail/errors I'm seeing this:

[21-Jun-2015 11:36:29] PHP Fatal error:  Using $this when not in object 
context in /usr/share/roundcubemail/program/lib/Roundcube/rcube_ldap.php 
on line 840
First instance occurred on 18/06.

Centos 6.6. Kolab 3.4