You need to have a fare available to go with the seat availability. Are there published M or S fares for your route and date?
Ah! Now I think we're getting somewhere!
My flight: DL260 MIA-LHR 01NOV shows:
On the Upgrade / Award page:
Z4
and on the Flight Availability page:
J9 C9 D9 I9 S8 Y9 B9 M9 H9 Q8 K4 L0 U0 T0 E0
(there's my S and M - so to speak)
but no S or M on the Fare Information Results page.
So I guess I now have a EF usability question... do you really have to go through all that or is there a simpler way?