Yamaha DTXpress/DTXplorer/DTXtreme

Hi there, I was editing kits and songs and then I noticed a black box 
with a letter d in it. Now the sounds are mixed up in my songs. At 
first I thought maybe my memeory is full and I deleted a couple, but I 
can't get rid of this sign and the sound settings for the midi 
channels and drumkit are stil OK.

Has anybody seen this before and knows what this means, thanks if you 
could share it.

Greetings from Santana