I'm having a little problem at the moment.

My Korg MS2000 doesn't start its arp when I hit it with an external midi-Command.
(and yes, my MS is turned to "external" in its midi-settings)
The Arp only starts when I hit the internal keyboard, but unfortunately not with external keyboards
e.g. a sampler...
The Mod Sequencer is running perfectly by the way.
How can I fix this problem? Are there any solutions or could it be, that the arp generally doesn't work external?
Hopefully somebody can help me.
All the best from Germany to u guys