SOLVED
Thank you Igor, you solved the issue for me.
I had one non-standard entry in my sites-available:
This is how I found it:
#for i in `ls`; do echo $i; grep listen $i; done
site1
listen 66.113.100.140:80;
site2
listen 66.113.100.140:80;
site3
listen 66.113.100.140:80;
site4
listen 66.113.100.140:80;
site5
listen 66.113.100.140:80;
site6
listen 66.113.100.140:80;
site7
site8
listen 66.113.100.140:80;
site9
listen 66.113.100.140:80;
site10
listen 66.113.100.140:80;
everybody has a 'listen' directive except the entry for 'site7'
#netstat -pant |grep nginx
tcp 0 0 0.0.0.0:80 0.0.0.0:* LISTEN 19915/nginx
tcp 0 0 66.113.100.140:81 0.0.0.0:* LISTEN 19915/nginx
#rm site7
#/etc/init.d/nginx restart
netstat -pant |grep nginx
tcp 0 0 66.113.100.140:80 0.0.0.0:* LISTEN 21884/nginx
tcp 0 0 66.113.100.140:81 0.0.0.0:* LISTEN 21884/nginx
SOLVED!
Thank you for your help!