Surely there is an easy answer for this

I have no errors in my preflight check. Although upong starting Nagios I receive the following
Error: Cannot open main configuration file ‘/usr/local/nagios/nagios.cfg’ for reading!
Warning: Cannot open log file ‘/usr/local/nagios/var/nagios.log’ for writing
Nagios 2.5 starting… (PID=17557)

Still cannot login to the web interface. Does anybody know how to solve this?
Thanks

Permissions on your files are wrong.