Is this with your 7800/9800 printer? After reviewing your order history, I see you last purchased Piezography Neutral ink in June 2009, so these inks are about five years old, therefore at least two years past their expiration dates...
How often have you been agitating your ink cartridges?
How often have you been using the printer vs. how long does it sit unused?
What repair has been done to this printer?
Have the dampers been replaced within the past three years?
Are you printing from Mac or Windows? What operating system version?
What paper(s) are you printing on, what what curve(s) are you selecting?
Please let me know so I can help resolve this and get you back to happily printing.
Best regards~ Dana