I'm having a really annoying problem on my Ubuntu laptop.
I noticed it today, after upgrading to Ubuntu 11.04, although I'm not entirely sure this is the cause as I played with my ssh keys a few days ago.
The problem is, whenever I try to ssh to ANY host I get the following error:

Read from socket failed: Connection reset by peer 

it's worked for me :)
Just try this bellow :

sudo vim /etc/ssh/ssh_config

Host *

SendEnv LANG LC_*

HashKnownHosts yes

GSSAPIAuthentication yes

GSSAPIDelegateCredentials no

Ciphers aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc 

You are done! Try SSH again!