Hi,
`slime-lisp-options' in slime.el uses `split-string' to parse the contents of `inferior-lisp-program'
This fails if the lisp program is in a path with spaces in it (such as executables in Windows). Quoting does not help.
One could instead use split-string-and-unquote:
(split-string-and-unquote "\"c:/Program Files (x86)/clisp-2.49/clisp.exe\" -E iso-8859-1")
("c:/Program Files (x86)/clisp-2.49/clisp.exe" "-E" "iso-8859-1")