But when I connect it via USB or via MIDI connectors to my computer ...

Please provide us more details on the MIDI connectors situation... It is not clear how you connect the MIDI connectors to Cubase Pro 8 - which says there are other pieces of gear involved in this situation. I might venture a guess if it was only via the USB connection but you clearly state that it occurs in either situation. So it begs the question, what else is involved (since you Mac does not have 5 pin jacks and there is no mention of an external device.

And because the problem occurs after 20 minutes and not immediately, please let us in on how long are the cables you are using... or any other (unusual) situation or external gear. How are you sending MIDI to the plug-ins? Basically, I'm asking are you using the Master Keyboard functions in the CP4 Stage or just Channels 1, 2 and 3?

Very curious. Let us know.

Thanks for your reply.

I apologize, I did not specify that I connected the MIDI output via a Yamaha UX16 USB-MIDI interface. I tried again in this way and it is verified again the same situation.
To avoid any possible interference I unplug the USB cable when using the MIDI and vice versa, but it happens anyway.
I tried it with a 180 cm and a 100 cm USB cable: same thing.
I tried to connect the USB cable to a built-in port, or to the hub of the computer keyboard: same thing.
I tried it using Channels 1, 2 and 3, and in Master Keyboard mode: same thing.
In Cubase I tried selecting as MIDI input "All MIDI Inputs" or "Yamaha CP4 STAGE Port1" (or "YAMAHA UX16 Port1"): same thing.
Then I tried selecting as MIDI output "Yamaha CP4 STAGE Port1" (or "YAMAHA UX16 Port1"), or a VST plugin (eg. Pianoteq): same thing.

The only other active device connected to the computer is a SpeedCom ADSL Ethernet router.

I just tried to use as a MIDI interface my FireWire MOTU Ultralite (I noticed that the CP4 STAGE transmits via MIDI even if it is set to USB), first connecting only the output connector (and seemed to transmit and work properly), then both (and unfortunately after a while it is stuck as usual).

Probably at a certain moment my CP4 STAGE receives a message (disturbing... from where? from DAW? from itself? from OS? from Core MIDI?...) that disconnects only the keyboard.

I tried to connect the USB cable to a built-in port, or to the hub of the computer keyboard: same thing.

Avoid using a hub

I just tried to use as a MIDI interface my FireWire MOTU Ultralite (I noticed that the CP4 STAGE transmits via MIDI even if it is set to USB), first connecting only the output connector (and seemed to transmit and work properly), then both (and unfortunately after a while it is stuck as usual).

The MIDI port on the CP4 Stage will transmit Midi at all times unless you plug in a USB cable and connect it to a host like a computer. It is at this point, the MIDI jack stops sending data.

The CP4 Stage seems to be transmitting properly.

Probably at a certain moment my CP4 STAGE receives a message (disturbing... from where? from DAW? from itself? from OS? from Core MIDI?...) that disconnects only the keyboard.

Please discover the nature of this message. The CP4 Stage when connected to a computer for MIDI recording should be set as LOCAL CONTROL = OFF. Local Control Off disconnects the CP4 Stage's key bed from the CP4 Stage's tone generator so messages must travel to and be echoed back from an active MIDI track assigned to the CP4 Stage.

It should only respond to data when the MIDI Track assigned to send Midi data OUT on the "Yamaha CP4 Stage Port 1" is selected and active.

Instead of setting the input for this MIDI Track to "All MIDI Inputs" please set it specifically to the "Yamaha CP4 Stage Port 1" - this way we eliminate any other device from addressing your CP4 Stage.

Thanks for your suggestions.
I will continue to investigate.

Hi.

I tried to check in Console utility if any system messages are transmitted at the moment of the hang, but I didn’t find anything special (apart from a suspect “kernel[0]: nspace-handler-set-snapshot-time”).

I tried to play the CP4 Stage alone, without connecting to the computer, and once again the keyboard is locked, but after a little more time, about an hour. I noticed that it happened while I was pressing the SPLIT and LAYER buttons, holding down the FC3A sustain pedal, something like the problem fixed in firmware update V1.01:

Fixed a problem in which, when turning on the layer part, pressing a key, then turning off the part while holding the sustain pedal, the sound of the layer part continues even though the key and sustain pedal have been released.

Perhaps the signal of FC3A interferes with turning on/off channels 2 and 3 (LAYER and SPLIT parts)?

But then, once restarted and played without USB connection, after a while it was blocked again without having touched any pedal or button…

I tried to connect the USB cable without turning off the CP4, and immediately the same thing happened (keyboard locked but controllers working). Console reported the following messages:

11/04/16 11:47:04,565 MIDIServer[305] WARNING: The Gestalt selector gestaltSystemVersion is returning 10.9.5 instead of 10.10.5. Use NSProcessInfo's operatingSystemVersion property to get correct system version number.
Call location:
11/04/16 11:47:04,613 MIDIServer[305] 0 CarbonCore 0x00007fff877c32b7 ___Gestalt_SystemVersion_block_invoke + 113
11/04/16 11:47:04,613 MIDIServer[305] 1 libdispatch.dylib 0x00007fff923b5e73 _dispatch_client_callout + 8
11/04/16 11:47:04,613 MIDIServer[305] 2 libdispatch.dylib 0x00007fff923b5d86 dispatch_once_f + 117
11/04/16 11:47:04,613 MIDIServer[305] 3 CarbonCore 0x00007fff8774c456 _Gestalt_SystemVersion + 987
11/04/16 11:47:04,613 MIDIServer[305] 4 CarbonCore 0x00007fff8774b6e3 Gestalt + 144
11/04/16 11:47:04,614 MIDIServer[305] 5 YAMAHA-USBMIDIDriver 0x00000001049fe997 _ZN16YmhUSBMIDIDriver11MatchDeviceEP9USBDevice + 217
11/04/16 11:47:04,614 MIDIServer[305] 6 YAMAHA-USBMIDIDriver 0x00000001049f7b06 _ZN20USBMIDIDeviceManager11MatchDeviceEP9USBDevice + 48

Then I used the MIDI Monitor utility: Note On/Off messages disappeared when the value of Hold Pedal has reached 127 and I pressed the LAYER button. No other strange message, apart from many Active Sense and Clock before and after.

Sorry, I don't know what any of that "Console" read out is supposed to tell you.

Please make sure (by physically looking at it) that your sustain pedal is plugged into the correct jack.
Did you try any of the suggestions I posted in the last post?
If so, what happened?

Hi.

Console is a Mac utility that shows OS messages, and I do not know if those are relevant.

Yes, I followed all your suggestions, I also tried to play without any pedal connected and is the same…

I've had enough, I give up. I really think that my CP4 is defective. I’ll bring it back to the store to get it replaced.

Thanks anyway for your help.