unable to set Metasound Input from blueprint

I am trying to implement a metronome. my bp handles the timing. 1ce per beat it creates a 2D sound, then sets the Input parameter from the beat number, then uses the Quartz system to Play the sound on the beat. The Input index chooses the WAV file from a pre-defined array of WAVs.

It works fine in that the metronome plays back. but it plays back using the default value of the ArrayIndex and not the value I tried to set in the blueprint. I am a noob on this stuff, any help is appreciated. I am attaching pix of the BP and MS


drovin