Are you trying to back-up your MPC zips to a computer? I've had that same problem where the computer only reads the first few characters in a name written on the MPC. If you have a lot of samples that all start with the same name the computer will only show the first one...... this is something I recently wrote about in another thread:
Well, my OSX Mac only reads the first partition of an MPC formatted disk & only the first few characters in a name.......which is annoying as I used to use really long names on the MPC.
I just need to be methodical putting those old zip disks straight into the Macs zip drive. Say I've got a bunch of drum sounds off an old Salsoul disco 12". I know I have sounds on the zip called Salsoul Kick, Salsoul Hat 1, Salsoul Conga 2 etc. The Mac will just list a single sound called SALSOUL. I load that one, listen to it & complete its name. Then I erase the one on the zip disc. The Mac will then show me the next sample with the same name SALSOUL & I go through the process again.
It is a bit safer to load those old zip disks on the MPC, rename them on that & then put them on the designated transfer zip disk.
The thread was:
http://www.mpc-forums.com/viewtopic.php?t=16775
The bad news is I think you probably have deleted those sounds the MPC cannot find. If you are lucky, you might have changed the name with the computer. Set the MPC to just load samples, not programs, so you can scroll through every sound on the zip & audition all of them if necessary. If you have lost any, this way you might find other sounds of yours you can use in their place.