I'm receiving an error message while the zabbix database is being upgraded:

12852:20170829:093103.768 Starting Zabbix Server. Zabbix 3.4.1 (revision 71734).
12852:20170829:093103.768 ****** Enabled features ******
12852:20170829:093103.768 SNMP monitoring: YES
12852:20170829:093103.768 IPMI monitoring: YES
12852:20170829:093103.768 Web monitoring: YES
12852:20170829:093103.768 VMware monitoring: YES
12852:20170829:093103.768 SMTP authentication: YES
12852:20170829:093103.768 Jabber notifications: YES
12852:20170829:093103.768 Ez Texting notifications: YES
12852:20170829:093103.768 ODBC: YES
12852:20170829:093103.768 SSH2 support: YES
12852:20170829:093103.768 IPv6 support: YES
12852:20170829:093103.768 TLS support: YES
12852:20170829:093103.768 ******************************
12852:20170829:093103.768 using configuration file: /etc/zabbix/zabbix_server.conf
12852:20170829:093103.773 current database version (mandatory/optional): 03030027/03030027
12852:20170829:093103.773 required mandatory version: 03040000
12852:20170829:093103.774 starting automatic database upgrade
12852:20170829:093103.776 [Z3005] query failed: [1005] Can't create table 'zabbix.#sql-9fb_63' (errno: 121) [alter table alerts add constraint c_alerts_5 foreign key (p_eventid) references events (eventid) on delete cascade]
12852:20170829:093103.776 database upgrade failed

I'm running CentOS 7, 5.5.52-MariaDB MariaDB Server

Can anyone help me out?

Thanks in advance,
Kevin