What does this error log mean?

[Joe]

Hi all
I installed Nginx 0.5.34 on FreeBSD 6.2 (AMD) as a load balance, and I 
defined the error log like:

error_log  /home/nginx/logs/crit_error.log  crit;

Today, I find the following error info from this error log file:

2008/01/20 20:46:46 [error] 2233#0: accept() failed (53: Software caused 
connection abort) while accepting new connection on 0.0.0.0:80
2008/01/20 20:47:39 [error] 2233#0: accept() failed (53: Software caused 
connection abort) while accepting new connection on 0.0.0.0:80
2008/01/20 20:53:15 [error] 2219#0: accept() failed (53: Software caused 
connection abort) while accepting new connection on 0.0.0.0:80
2008/01/20 20:54:33 [error] 2219#0: accept() failed (53: Software caused 
connection abort) while accepting new connection on 0.0.0.0:80
2008/01/20 20:54:56 [error] 2219#0: accept() failed (53: Software caused 
connection abort) while accepting new connection on 0.0.0.0:80
2008/01/20 20:55:35 [error] 2219#0: accept() failed (53: Software caused 
connection abort) while accepting new connection on 0.0.0.0:80
2008/01/20 20:56:11 [error] 2215#0: accept() failed (53: Software caused 
connection abort) while accepting new connection on 0.0.0.0:80

The number 2233,2219 should be the PIDs, what does the number 53 mean 
here? and what's the root cause which will trigger this kind of error?


Thanks
Joe