EmulatorII-list

Hey guys, just got my first emulator II today... I'm going thru an online manual but I'm sure 
this won't be my last question here as I'm still learning all the functions..

It came with around 50 disks and I've only got 11 of them to work...
The two main error messages i get are "Null Preset Disk Read Error" and "HD MiniS 20 R2.6" 
<---I get that one the most. Does anyone know what these mean? Also I read in the online 
manual that slider A is supposed to scroll through the sounds on the disk but I havent gotten 
it to do that.. Any help would be appreciated! Thanks in advance