A couple of things to try, Find a default COS (One that has not been changed before) and add just the options necessary for the divert, ie trunk to trunk, public dpnss etc, Just the bare minimum needed. Assign to the users in question and try again, Often you can miss an option in cos that should not be on and this is the simplist way to prove it.
With regards to the nummber you put in, the leading digit should be in the ARS form leading digits. ie if you dial a 9 to get out then 9 should be in this form, any error checking against the number is done by referencing this form.