Digital BW, The Print

Hi,
I bought a C86 and MIS inks not too long ago. After a few nice prints 
(in which the eboni cartridge ran out very quickly), i installed a new 
eboni cartridge in the black slot and noticed that there was still 
quite a bit of ink in the old cartridge.  With the new cartridge, I 
had one successful print before my printer driver told me the black 
cartridge is out of ink. Now I can't print. Any suggestions?

thanks

Jim