Insufficient memory issue

Hello, I am very new to the world of MPC, and I was recently gifted an old mpc500. I am trying to load samples and assign to pads, but when I attempt to assign to pads, i am prompted with an "insufficient memory" message on the lcd. I have deleted a lot of samples to make room for a 5 second sound clip, and I am not sure why it will not assign my samples to my pads. any help would be appreciated, and i am sorry for asking the annoying n00b questions in advance.

Do you have 16mb or 128mb of ram installed?

If you don’t have Akai brand RAM, you’ll need a stick of popular brand of 256MB RAM for the MPC500 to show the full 128MB.
I know that sounds weird but you can thank Akai for that logic.