Problems Starting Garage Band App

I just bought an iMac OSX 10.7.4. The already installed Garage Band App had worked fine for the first weeks, it is up to date. Now, When I try to open Garage Band appears a message:

"MIDI timeout

GarageBand has detected a MIDI timeout. Please restart your computer, then relaunch GarageBand.

If the problem persists, update the drivers of all connected MIDI devices (including audio drivers with MIDI functionality) to the latest version. For instructions on removing older drivers, consult the manufacturers' documentation."

I do not know much about Midi and stuff. What can I do to fix the problem?

The app says: "Application not responding"

Thanks a lot.

Jhoger