When we try to access /sld/fun it is generally redirected to this URL
http://<Hostname>:<Port>/webdynpro/resources/sap.com/tc~sld~wd~main/Main?functionality=true
However, in our case, it is getting redirected to
http://<Hostname>:<Port>/webdynpro/resources/sap.com/tc~sld~wd~main/Main
I just added "?functionality=true" at the end of the URL and that opened up the functional configuration wizard and everything else works just fine from there.
It is just a work around. Hope it helps.