Can't save files in internal zip disk

I've just installed an inetrnal zip disk to my mpc 2000 xl. I have no problems loading the samples and sequences, but when i want to save it (or even create a new folder) keeps telling me write protect.
What is the problem?
Thanx

turn off the 'write protect' switch on the back of the zip disk

I may sound dumb but I cannot find! It's a zipp 100 MB (my internat zip it's a 750 Mb) could be this the problem?

Zip 750 drives cannot write to 100MB disks. More info on www.iomega.com

Thanx a lot for the info!