The client version of SciFinder will be retired by CAS on June 30, 2011. Between now and June 30th, access to the client will be decreased and access to the web will be increased in an effort to encourage users to transition to the web.
After June 30th, you will have to use the web version of SciFinder. To use the web version, you must first register. Instructions are here. Once you have registered, you can go directly to SciFinder.