Digital BW, The Print

From one day to another I have problems with my Epson 1160 
with Piezo driver. I get a sort of steps (banding) in the middletone 
areas, f.ex. skintone in a portrait. It looks like it is totally 
overexposed in the highlight areas.  I made axactly the same 
print ya few days ago and it was perfect. 
Can someone tell me what this is? I have never had these 
problems before. Is it banding? And is it a problem with the 
printer or the software?  How can I get rid of this?
I use PiezoToneWN and Epson Archival matte paper.
Nozzle checks is OK, have also checked the alignment, it was 
OK.

Bjorn