You have probably created a MIDI loop, where data coming out from the computer somehow is infinitely fed back to its input. Try unplugging cables, reprogramming the MIDI Patchbay and turning off "MIDI Thru" in your devices.
MIDI error in deviceIf for some reason, you get a MIDI Error message in the display on one of your devices, you must "reset" it before you can go on. This is probably most easily done by turning the unit off and then on again after a few seconds, but please note that this might make you lose settings that have not yet been permanently stored in the device.
Problems when using an MPU compatible interfaceWe strongly recommend you to use the MPU driver written by Steinberg and included with the Cubase, rather than the one provided with Windows.