Which host are you using?
edit: never mind, I see it in your signature. That all looks pretty reasonable... Does this happen in Platinum with just one instance? Or are you working in a project with many instances?
edit again: never mind, I can see you tried the micro host and even that drops out. That's bizarre, since that program is pretty low key. Does this happen with any preset? Or just certain presets?
THIRD EDIT:
Sorry about these. What you're describing sounds like our authorization protection; are you dropping out, or are you just randomly getting silence? We do that when the synth isn't authorized (you can verify you've been authorized by clicking the Z2 logo in the top left and looking at the about screen; your serial number should be displayed.) We also prevent you from saving your own presets, so if you can't do this (a window pops up and says you can't) then that's the root issue.
Now, as for why you aren't authed, I believe several users were running into those kinds of issues. If you can verify that it is the authorization we can start from there.