could also be this
https://www.cakewalk.com/Support/Knowledge-Base/2007013179/I-cannot-hear-MIDI-playback what driver mode are you using for your Alesis I02 ? are you using MME ?
I only ask because if you mixing driver modes with the zoom driver, this might cause internal hardware routing issues.
which we see a lot of here on this forum.
PS- you might want to add your specs your signature.
I know what your using (the zoom + the I02) but other do not and will more than likely skip over your threads not knowing your set up. I know often when im helping people if there is no info listed (hardware, audio card, Windows os type) sometimes I will not even bother. So this betters your chances of good forum users helping you out.
just add it to your signature. (windows OS, audio card, exc). the more the better.
this will only help you out.