Bad SSH2 cipher spec error

I'm trying to scp data between 2 Solaris systems: 

Source server: Solaris 10 / Sun_SSH_1.1 / OpenSSL 0.9.8.a.
Destination server: Solaris 8 / OpenSSH_4.2p1 / OpenSSL 0.9.8a

Using scp -p, I can move files from the source to the destination
without any problems. However, from time to time, the copy fails with
the following message:

/etc/ssh/ssh_config line 21: Bad SSH2 cipher spec 
'aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour,aes192-cbc,aes256-
cbc'. 

What can I do about this and how can I go about debugging the problem?
How can I verify that the ciphers listed in ssh_config are usable
ciphers between the source and destination serves? 

- CDM
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