i found in /var/log/kolab-webadmin/errors:

PHP Fatal error:  Call to undefined method LDAP::domain_root_dn() in /usr/share/kolab-webadmin/lib/Auth/LDAP.php on line 119

after a long study i found the problem that the package php-Net-LDAP3 from kolab3.4 is still installed.

i solved the problem with:

yum shell
remove php-Net-LDAP3
install php-kolab-net-ldap3.noarch
run

the documentation should be updated?

moreover, i found 3 packages from kolab3.4 repo still installed:
mozldap.x86_64 6.0.5-37.1.el7.kolab_3.4 @Kolab_3.4
mozldap-tools.x86_64 6.0.5-37.1.el7.kolab_3.4 @Kolab_3.4
python-icalendar.noarch 3.8.2-7.1.el7.kolab_3.4 @Kolab_3.4

should i clean them or update them?