Browser not connecting to database

[themetman]

I am trying to look at my Zabbix Server using Firefox. I have had it running for years with no problems. I can log in fine, but no data is showing.
I have much the same problem as https://www.zabbix.com/forum/zabbix-...entory-objects but I have tried the solutions there and they do not work for me.
I have the Zabbix Server version 02040000 running in Ubuntu 16.04lts and that is showing no errors. I have looked at the mysql database using phpmyadmin, and all is well there.
I have had a look at the Server Log and there are several errors relating to some agents, but not all agents. here is an example:

cannot send list of active checks to [10.6.77.40]: host [picluster.fsoft.nnet] not found

If I run this

zabbix_get -s picluster.fsoft.nnet -k system.cpu.load[all,avg1]

I get a result, so things must be working. I have restarted the zabbix-server and apache services, to no avail.
Has anyone any idea how I can get the browser to wake up?

[themetman]

I gave up in the end, having spent agens looking around for a solution. I could see no reaason fro it in the Apache, MySQL or Zabbix logs anywhere.
I reinstalled upgrading to version 4 as well.