Problem with public key ssh login

Question

Weird problem just appeared. Home computer has two accounts (A and B). I allow ssh login to both accounts via public key login (ssh-keygen). Two remote computers with accounts A' and B' on one, and A" and B" on the other.
I can ssh into the home computer account B from account B' on one computer. I can log into the home computer account B from account B" on the other computer. I cannot ssh into the home computer account A from either A' or A", but I could last week.
Here is what the .ssh directories look like:
Home computer, account A:
total 8
drwx------ 4 userA groupA 136 Jan 30 11:51:38 2006 .
drwxrwxr-x 25 userA groupA 850 Nov 8 20:05:58 2006 ..
-rw-r--r-- 1 userA groupA 1216 Jan 10 13:20:20 2006 authorized_keys2
-rw-r--r-- 1 userA groupA 447 Sep 25 15:28:42 2006 known_hosts
Home computer, account B:
total 16
drwx------ 5 userB groupB 170 Oct 2 09:52:02 2006 .
drwxr-xr-x 23 userB groupB 782 Nov 9 08:26:03 2006 ..
-rw------- 1 userB groupB 6148 May 19 17:54:58 2006 .DS_Store
-rw-r--r-- 1 userB groupB 1228 Jan 10 13:24:15 2006 authorized_keys2
-rw-r--r-- 1 userB groupB 242 Oct 2 09:52:02 2006 known_hosts
Remote computer 1, account A':
total 16
drwx------ 6 userA' groupA' 204 Nov 9 09:55:12 2006 .
drwxr-xr-x 29 userA' groupA' 986 Nov 9 09:41:21 2006 ..
-rw-r--r-- 1 userA' groupA' 41 Mar 13 12:13:17 2006 config
-rw------- 1 userA' groupA' 736 Nov 20 13:38:54 2005 id_dsa
-rw-r--r-- 1 userA' groupA' 607 Nov 20 13:38:54 2005 id_dsa.pub
-rw-r--r-- 1 userA' groupA' 246 Jan 10 09:41:27 2006 known_hosts
Remote computer 1, account B':
total 16
drwx------ 5 userB' groupB' 170 Nov 9 08:23:04 2006 .
drwxr-xr-x 18 userB' groupB' 612 Nov 9 09:52:11 2006 ..
-rw------- 1 userB' groupB' 6148 Nov 9 08:23:04 2006 .DS_Store
-rw------- 1 userB' groupB' 668 May 25 08:51:51 2006 id_dsa
-rw-r--r-- 1 userB' groupB' 2481 Oct 30 09:00:57 2006 known_hosts
Remote computer 2, account A":
total 12
drwx------ 5 userA" groupA" 170 Jan 25 10:59:54 2006 .
drwxr-xr-x 20 userA" groupA" 680 Nov 9 08:19:30 2006 ..
-rw------- 1 userA" groupA" 736 Jan 10 13:14:16 2006 id_dsa
-rw-r--r-- 1 userA" groupA" 609 Jan 10 13:14:16 2006 id_dsa.pub
-rw-r--r-- 1 userA" groupA" 3376 Oct 31 19:48:25 2006 known_hosts
Remote computer 2, account B":
total 12
drwx------ 5 userB" groupB" 170 Jan 25 11:41:48 2006 .
drwx------ 22 userB" groupB" 748 Nov 9 10:33:00 2006 ..
-rw------- 1 userB" groupB" 736 Jan 10 13:11:50 2006 id_dsa
-rw-r--r-- 1 userB" groupB" 615 Jan 10 13:11:50 2006 id_dsa.pub
-rw-r--r-- 1 userB" groupB" 2947 Nov 7 10:18:27 2006 known_hosts
I had copied the A' id_dsa.pub from remote computer 1 to the home computer account A authorized_keys2, then I copied the A" id_dsa.pub from remote computer 2 and had appended it to the home computer account A authorized_keys2. I had done a similar thing with accounts B', B", and B on their respective computers.
All worked great for many months, until today, when ssh connections from A' or A" into A give me the dreaded
Permission denied,gssapi-keyex,gssapi-with-mic) error message. Pretty certain that it was as recent as earlier this week I made the A'-->A ssh connection and all was well. Meanwhile, ssh connections from B' or B" into B still work fine.
As near as I can tell, file ownerships and permissions look okay. While ssh'ed into B from B' I even did a
cat /Users/userA/.ssh/authorized_keys2
and then in another Terminal window, local to the remote computer, I did a
cat /Users/userA/.ssh/id_dsa.pub
In the terminal windows, each key wraps over about five-and-a-half lines, and I spotchecked like the last half-dozen characters, on each Terminal window line, of remote computer 1, account A' id_dsa.pub and the first pub key entry in authorized_keys2 in home computer account A. They all match.
I even keep a clone backup of my hard drive, and the date/timestamp of /etc/sshd_config hasn't changed (although, I'm a bit mystified why it is dated as recently as it is -- Sep 29 2006 -- don't remember doing anything to it)
So, I'm really confused, and not sure what to try or where to look next.
2001 Quicksilver G4 (M8360LL/A)   Mac OS X (10.4.8)  

Answer 1

Hi j.v.,
Home computer, account A:
total 8
drwx------ 4 userA groupA 136 Jan 30 11:51:38 2006 .
drwxrwxr-x 25 userA groupA 850 Nov 8 20:05:58 2006 ..
The parent directory ".." of the directory ".ssh", i.e. home directory of account A, is group-writeble. SSH considers this as "insecure". You should make it writable only by the owner.
A@Home$ cd (cd to the home directory)
A@Home$ chmod g-w .
HTH
PowerMac G4   Mac OS X (10.4.7)