Digital BW, The Print

I've been using MIS VM inks for about two years now. Until recently I 
was very pleased with the results using either MW (medium warm) or NC 
(neutral cold), I never used the other two options. I began with the 
1160 printer and switched to the 1280 roughly a year ago, using the 
Roark curves for each. For about the last four or five months I've 
been unable to get a good NC or MW print. The NC prints have a bluish 
or purplish tint, the MW prints have purplish brown tint. 

Am I the only one having this problem? Is it possible that I've been 
getting bad cartridges (I don't print a whole lot, I've probably gone 
through three or four sets of cartridges while having this problem). 
Is it possible that some setting can be changed to fix the problem (I 
use the various settings suggested by Paul Roark).

Any thoughts, help, suggestions etc. would be appreciated. I can't 
continue to use these inks if the results I've been getting can't be 
corrected but I hate to give up on them after getting such good 
results until recently.