Solaris

Yes, i'm working in the same VLAN so that is not the problem. I received the same ssh login problem for other server also, which was also at the same patch level as this server and when i patched that.
Checked the syslog and found same error: fatal: matching cipher is not supported: aes256-ctr
Uncommenting the line containing ciphers and restarting the ssh service, made it work.

Not sure if youve resolved this yet. On solaris 10 releases prior to 10/08 installation there is no SUNWcry package (crypt). Once you update to kernel rev 139555-08 this problem will surface.
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Try pkginfo -l | grep SUNWcry

also check if patch 141742-02 is installed ( showrev -p | grep 141742-02 )
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if you do not have SUNWcry and DO have the above patch installed, pop a sol 10 10/08 CD/DVD and do a pkgadd of SUNWcry, then, remove and re-add 141742-02. Problem should disappear.
Newer releases of Sol10 came with SUNWcry so are no issue.
All above is based on SPARC, so if using opensolaris, or i386 sol10, you'll need to research the pacth number (same issue exists, but diff patch rev between arch).

Quick n nasty workarounds:
1 - if using putty, when opening a new session, go to the ssh section, and in the box titled "Encryption selection cipher" move blowfish to the top and try again.
2 - server side workaround:
Change the two config files /etc/ssh/ssh_config and /etc/ssh/sshd_config and add the following line:

Ciphers aes128-ctr,aes128-cbc,arcfour,3des-cbc,blowfish-cbc

then restart ssh

FYI, obviously by implementing the server side workaround,
you are leaving your system in a weaker state as far as
encyption goes.

CAVEAT: Make sure you read the pacth install instructions - can't
remember if it requires a reboot when removing/re-adding the patch.

Hi... when you apply the patch, is it need to boot to single mode?

As my caveat states, make sure you read the patch install instructions. Can't just give you all the answers
Having said that, SUN always recommend to install patches in single user mode. Sometimes that's not so practical, and I've generally applied patches running in multiuser with no issues esp if it's not a kernel patch.
If it goes wrong though, you wear it, because you didn't follow SUN's advice.

Cheers,

That is always the recommended method.