SSH uses SSL for its encryption, the two on a given system need to be of matching (or near enough) build versions. SSH and SSL on Solaris 10 are Sun supplied so can be reinstalled from the Solaris 10 DVD. To determine what the package names are that provide SH and SSL run:
The last column will show the names of the packages the SSH and SSL components came from, the names of which usually start with SUNW.
I would value others confirming these steps to resolve the problem but I suggest:
Confirm that the SSH and SSL packages are available on your Solaris 10 DVD.
Back up your system,
Back up your /etc/ssh/ssh_config and /etc/ssh/sshd_config files where they can be easily retrieved if you have changed them from the default.
Reboot into single user mode.
Remove the current SSH and SSL packages.
Mount the DVD (you will probably need to start the volfs service (vold) in order to get the DVD to mount automatically).
Reinstall the packages.
Reinstate your /etc/ssh/ssh_config and /etc/ssh/sshd_config files.
Reboot.
Apply any Sun patches relevant to these packages.