[Pound Mailing List] e500 response error read

Hi Guys
I'm having a problem and my site is currently down.

Pound has been working fine for me for months and I've had no reason to change the config.

Today, suddenly my site went down.  Accessing the site flooting.com gives a 

"An internal server error occurred. Please try again later."

However there are no error messages in the site logs.  I was confused.
It turns out, it's pound that is returning the error.  Pound is saying it's unable to connect to the web servers that it's balancing requests over, however
the servers are there and I can access them directly.

The networks are up, everything is fine.

The error message is;
Aug  8 18:12:46 six pound: (f7282b70) e500 response error read from 192.168.8.51:80/GET /login HTTP/1.1: Connection timed out (15.016 secs)


There has been no change to the pound configs for a long time.

I've bumped the log output up, but that's the only message that is output.  which is strange.
also i have an EMERGENCY host configured (and I'd consider this an emergency) however pound is not redirecting to the emergency page.

From the point of view of the web servers, the request is never arriving at the servers.  
I'm dead in the water and I can't see anything that may have changed.  In desperation I've rebooted everything.  That didn't help.

Has anyone ever seen anything like this?

Thanks
Mark

Configs are:

######################################################################
## global options:

User		"www-data"
Group		"www-data"
#RootJail	"/chroot/pound"

## Logging: (goes to syslog by default)
##	0	no logging
##	1	normal
##	2	extended
##	3	Apache-style (common log format)
LogLevel	2

## check backend every X secs:
Alive		30

## use hardware-accelleration card supported by openssl(1):
#SSLEngine	"<hw>"

# poundctl control socket
Control "/var/run/pound/poundctl.socket"


######################################################################
## listen, redirect and ... to:

## redirect all requests on port 8080 ("ListenHTTP") to the local webserver (see "Service" below):
      # Main listening ports
ListenHTTP
   Address 91.187.69.155
      Port    80
      RewriteLocation 2

# Roundcube
Service
     URL         ".*roundcube.*"
     BackEnd
       	  Address 192.168.8.45
          Port    80
     End
End

# Flooting.com
Service
    HeadRequire   "(Host: flooting.com|Host: www.flooting.com)"
       BackEnd
           Address 192.168.8.51
           Port    80
       End
       BackEnd
           Address 192.168.8.52
           Port    80
       End
       Emergency
          Address 192.168.16.12
          Port 8080
       End
End