Special invite including musical drama producing no effect (11)
I believe the answer is:
inoperative
'producing no effect' is the definition.
'special invite including musical drama' is the wordplay.
'special' indicates an anagram.
'including' is an insertion indicator.
'musical drama' becomes 'opera' (I've seen this before).
'invite' anagrammed gives 'intive'.
'intive' going around 'opera' is 'INOPERATIVE'.
(Other definitions for inoperative that I've seen before include "Not in working order" , "It's useless" , "with no effect" , "Anna -, Russian poet (Requiem)" .)