Thanks for the reply and suggestion. Sorry it's taken me a while to respond.
I can see the ink through the translucent cart wall and there still appears to be plenty. I suspect the problem has arisen from some kind of airlock I may have created in the cart by popping plugs in and out; or by some resetting of the cart chip.
I'm now in contact with support at MIS, so should be able to figure it out.
Again, thanks for the response.
Regards,
Harold