thanks tobyink, but i updated my openSSH to the latest one i.e. 6.0 and openSSSl is also compatible with that.
My ubuntu version is bit old i.e. 10.10.
Is this could be the culprit? But again it 's not very much related with that error............right?
Upgrading to a newer version of OpenSSL will not help you generate a 2048 bit DSA key. If you want a 2048 bit DSA key, then you need to downgrade to a very old version. (Or use something else to generate it - in which case it's unlikely SSH will accept it.)