ssh_exchange_identification: Connection closed by remote host

[petesea at bigfoot.com]

I'm randomly getting the following error on a server from various remote 
hosts:

   ssh_exchange_identification: Connection closed by remote host

The server is running OpenSSH 4.5p1 w/GSSAPI Key Exchange patch.  The 
hosts connecting to it should all be using OpenSSH 5.0p1 w/GSSAPI Key 
Exchange patch and using gssapi-keyex authentication.

Normally, when I've seen this error, it means access to the SSH port is 
blocked by TCP wrappers or something like that, but I'm sure that's not 
the case here since /etc/hosts.allow and /etc/hosts.deny haven't changed 
for quite some time.  Also, the failures are random from many different 
remote hosts and I can try a connection from a host right after it's 
failed and it will work.

Under what other conditions might I get this error and how can I track 
down what's causing it?