Recording from my keyboard to my MPC

I been recording from my keyboard to my MPC abd I get one MIDI track on my MPC if I add another track my keyboard says MIDI buffer full. What the hell does that mean and how can I correct it. Any help would be great!

Thanks,

Acq1

What kind of keyboard are u using?

I have a Roland JX-305. It's kinda old but it works great (nice sounds).