Given the title, I realize there's probably not a large number of people who will have encountered my problem, but here goes:
I use Producer 8.5 and recently began controlling it with the ProjectMix - a great tool. I have an Alesis keyboard synth (for its weighted keys when playing piano parts), and use an Edirol PCR 500 to play soft synths. The Alesis is connected to the ProjectMix via midi cables; the Edirol is connected directly to the computer via USB.
Producer sees all the ProjectMix inputs/outputs and the Edirol inputs/outputs. The problem is, when both are connected and played, there is midi activity showing (visible in the track and audible in the monitors) in the eye-straining little indicator on the task bar when playing the ProjectMix/Alesis combo, but there is no midi activity indicated when I play the Edirol. And there's no activity inside the subject track with the Edirol either, even though Producer looks like it recognizes and connects to both devices.
Disclosure: I'm fairly smart and intuitive about a lot of technical things: MIDI ain't one of 'em.
Your helpful thougths will be greatly appreciated.