Digital BW, The Print

Has anyone experienced this problem, and if you have can you offer any
explanation at all?

I'm printing 15 prints for a large pix exchange, and the first 13 were
identical. The last 2 were much darker and with a heavy cyan cast over
the whole print. Absolutely nothing was changed between 13 and 15. The
printer was set to print 15 images, and the last 2 turned out that way.
Bottles of ink are nearly full, heads and nozzles clean, no banding or
other problems.

Inks were Generations Color inks, 1160 printer.

Thanks

Jerry