can't write to ssh known_hosts file

Awhile back I did a complete restore from backup of an MBP. Since then this machine's ssh client can no longer will write to the ~/.ssh/known_hosts file:

The authenticity of host 'dhcp167 (172.31.0.167)' can't be established.
DSA key fingerprint is 66:3d:0c:31:e0:07:09:6b:21:f9:8c:79:40:50:01:45.
Are you sure you want to continue connecting (yes/no)? yes
Failed to add the host to the list of known hosts (/Users/dnewman/.ssh/known_hosts).

I have write access to this file:

dhcp130:~ dnewman$ ls -l /Users/dnewman/.ssh/known_hosts
-rw-r--r--@ 1 dnewman staff 36439 Sep 26 17:51 /Users/dnewman/.ssh/known_hosts

How to remedy this error?

thanks