I got the same problem, and it got solved by this way:
open:Window->Preferences->Lisp->Implementations
if (you install cusp in the same folder of plugin) then
unselect "use a lisp sitewide installtion"
else
select "use a lisp sitewide installtion"
add path of sbcl.exe to windows env_var $PATH
add new windows env_var: $SBCL_PATH, set it to path of sbcl.exe