Great work!

macling66, check directory permissions. checkresults should have write access for www-data user.

# ls -ld /var/lib/nagios3/spool/
drwxr-x— 3 nagios nagios 4096 Jun 28 2013 /var/lib/nagios3/spool/
# ls -ld /var/lib/nagios3/spool/checkresults/
drwxr-x— 2 nagios nagios 12288 Oct 30 12:34 /var/lib/nagios3/spool/checkresults/
# chown nagios.www-data /var/lib/nagios3/spool/checkresults/
# chmod g+w /var/lib/nagios3/spool/checkresults/
# ls -ld /var/lib/nagios3/spool/checkresults/
drwxrwx— 2 nagios www-data 12288 Oct 30 12:34 /var/lib/nagios3/spool/checkresults/