Hi, I just tried lispworks 5.1/linux (released today) with Slime CVS HEAD. I'm not a Slime hacker, but it appears that the argument to swank-backend::lispworks-severity in this version of LW can be a dotted list of the form: (#<CONDITIONS::SIMPLE-STYLE-WARNING 200BF8A7> . 15798) Thus the etypecase in lispworks-severity can fail. So, a naive patch: (defun lispworks-severity (condition) (cond ((not condition) :warning) (t (etypecase #+:lispworks5.1 (car condition) #-lispworks5.1 condition (error :error) (style-warning :warning) (warning :warning))))) I don't doubt that this should be taken care of elsewhere, before the call to lispworks-severity. The list structure seems to have consequences elsewhere. e.g warnings now look like this: -+ Warnings (1) `-- (*ZIPPY* assumed special in SETQ . 15798) -- Best regards, - Peter