aggregate I/O problems

[utmedusmc]

I have a Mac Pro OS X Lion 10.7.4 system, audio box presonus and downloaded pro Tools 10 yesterday. The sound wouldn't come out of my computer speakers (hooked up via USB) only the computer itself. So, I went to the Mac Launchpad and midi input screen to change audio device to my speakers and clicked off of everything else. Then I got "could not create a new document because assertion in "/Volumens/Develompent/ws.ProTools_10.1.2/AlturaPorts/DFW/MacBuild/..?views?UMenus.MacOS.mm", line 1351 message. What does that mean? It won't even let me open a new session. I changed the settings again, and then it said it can't support a 4.41KHz setting? Please help, I was working fine yesterday before I started messing around with the Mac midi interface.

[Steve Marcotte]

In ProTools, try going to Setup->Playback Engine and choose your output device from the drop down list at the top.