Dragan,
The SSH version 2 feature is not supported in the above IOS (IP PLUS IP 3DES).
Try upgrading to c2600-advsecurityk9-mz.12.3-4.T.bin which has SSH v2 server support. This is the least version as per feature navigator to support it.
www.cisco.com/go/fn
HTH, rate if it does
Narayan
