This message comes up in two steps with Canon bubblejet printers. First there is a warning, then the printer refuses to work at all.
What has happened is that the software has determined that sufficient head cleaning/purging has taken place to fill the waste ink absorber with waste ink.
[It also means that you have spent rather a lot of money on ink, and that you may have used the printer more than was altogether prudent for a home/small office machine.]
This problem can not be solved by the user. You must take or send it to a service centre, where a technician will remove the old ink absorber, clean up any internal ink mess (a job seemingly made much more difficult and messy if the customer has been using cheap non-original inks) and enter a reset code to clear the “ink absorber full” condition.
[With some printers, no internal cleaning at all was required, while others, when unpacked, were plastered inside and out with black waste ink, and had to be completely dismantled and the parts hosed down and air dried before re-assembly. We suspected that the use of cheap inks caused this by gumming up the absorbers, hence the bad attitude you may encounter in the repair shop if you use cheap inks.]
Admittedly many users find the “waste ink tank full” very annoying, and one has some sympathy with their point of view, but alternative solutions would add to the point-of-sale cost, or be more messy and generate undesirable household waste.
[No you can not solve the problem by making your own absorber, or washing out the old one. DIY or recycled absorbers don’t work. Nor is it wise to enter the reset code, even if you can get your hands on it , without having the clearly well-used printer serviced.]