It appears that the name of the 'contrib' sub-directory was misspelled when added in recent changes to 'slime.el' and 'slime-autoloads.el'. The spelling lists the directory name in the plural ("contribs") instead of the singular ("contrib"). This causes the Emacs LOAD-PATH variable to be set incorrectly.
cvs diff slime.el Index: slime.el =================================================================== RCS file: /project/slime/cvsroot/slime/slime.el,v retrieving revision 1.905 diff -r1.905 slime.el 76c76 < (expand-file-name (concat slime-path "contribs"))) ---
(expand-file-name (concat slime-path "contrib")))
cvs diff slime-autoloads.el Index: slime-autoloads.el =================================================================== RCS file: /project/slime/cvsroot/slime/slime-autoloads.el,v retrieving revision 1.4 diff -r1.4 slime-autoloads.el 44c44 < (expand-file-name (concat slime-path "contribs"))) ---
(expand-file-name (concat slime-path "contrib")))