When "SEND TEST" buttons are greyed out there is no notification as to what is missing from required fields to be NOT NULL. By default if "Opt-Out" token is not included in the message the "Opt-Out" response is left NULL but is still a required field that cannot be left empty. Choosing the only default brings all the buttons active. Please advise?
There shouldn't be any connection between the "Opt-Out"/"Unsubscribe" token and the field "Responses: Opt-Out Message". Both are required.
If the "Opt-Out" token (or "Unsubscribe" token) is missing, then you should get a very loud error message. (The token is generally provided as part of a header, footer, or message template, so that you don't have to put it in explicitly.)
The field "Responses: Opt-Out Message" should be filled in by default. If it's not, then perhaps someone removed the default. Try navigating to "Mailings => Headers, Footers, and Automated Messages". Edit one of the "OptOut" messages and set it as default.
I found a couple more situations that the greyed out button can appear which may be less than obvious
if there is no Resubscribe Msg set on the Response tab (no alert is currently provided
if you put in a Subject, but then decide to switch to using a Template that has no Subject then the one you added gets wiped