Failing to login to GUI with admin account

Maybe it has something to do with file permissions. Then you can see messages like this in the /var/log/tomcat/catalina.out logfile:

log4j:ERROR setFile(null,true) call failed.
java.io.FileNotFoundException: /var/log/webui.log (Permission denied)

I've seen systems where the settings of the /var/log partition was set incorrectly. Like:

[root@localhost:Active:Standalone] etc  ls -ldZ /var/log
drw-r--r--. root root system_u:object_r:var_log_t:s0   /var/log
-rw-rw-r--. root tomcat system_u:object_r:var_log_t:s0   /var/log/webui.log

Fix it like this:

 chmod 0755 /var/log
 tmsh restart sys service tomcat

Maybe not a bad idea to reboot the whole box.