I downloaded slime 20091111 snapshot and slime clisp works perfectly but when I followed the instructions in swank-mit-scheme.scm and I try to start slime with M-x mit-scheme,I got:

-------------------------- Unbound variable: :swank-asdf [unbound-variable]

Restarts: 0: [use-value] Specify a value to use instead of :swank-asdf. 1: [store-value] Define :swank-asdf to a given value. 2: [abort] Return to SLDB level 1. 3: [use-value] Specify a value to use instead of swank:swank-require. 4: [store-value] Define swank:swank-require to a given value. 5: [abort] Return to SLIME top-level. --more--

Backtrace: 0: ;Unknown (methodless) #[stack-frame 14] 1: :swank-asdf 2: :swank-asdf 3: (eval (cons* (car sexp) socket (cdr sexp)) swank-env) 4: (set! result (eval (cons* (car sexp) socket (cdr sexp)) swank-env)) 5: (with-simple-restart (quote abort) (format #f "Return to SLDB level ~a." level) (lambda () (dispatch (read-packet socket) socket level))) 6: ;unknown compiled code 7: ;unknown compiled code 8: ;unknown compiled code --more-- --------------------------

The version of mit-scheme I used is 7.7.90+20090107-1,which is supposed to work with slime as described in swank-mit-scheme.scm.I can verify that The file /usr/share/emacs/site-lisp/slime/contrib/slime-asdf.el has been successfully loaded

what could possibly be wrong? I'm quite a newbie on scheme. I would appreciated that someone can help me out.