Digital BW, The Print

I tried printing after not using my 2200 printer for awhile. I get an 
error message that the printer does not recognize one of the 
cartridges, which is a UT7 cartridge. When I last printed several weeks 
ago, there was no such problem. In fact, the cartridge that isn't 
recognized now is probably about half empty from using it successfully 
to print. Any ideas? Thanks. 

Paula Berg