Which versions of nethserver-squidguard and ufdbGuard are installed? It was updated recently, see Ufdbguard conflicts between attempted installs of nethserver-squidguard
[root@server ~]# rpm -q nethserver-squidguard ufdbGuard
nethserver-squidguard-2.0.0-1.ns7.noarch
ufdbGuard-1.34.6-2.el7.x86_64
Please check the log for more error information:
cat /var/log/ufdbguard/ufdbguardd.log | grep -i "fatal error"
ufdbguard does not use mysql AFAIK.