going potty on the floor

Question
We have two cats that have been with us all their lives (brother and sister - both neutered) 8 yrs. old. They are in good health. We use two litter boxes for them, and until recently they have never had any "accidents". Lately, however, even if the boxes are clean, one of them has been "pooping" right outside the box on the carpet. I have gotten new boxes, used carpet refreshner powder, changed the type of litter...to no avail. What's the problem.

Answer
Many times when litter box habits are changed, it has something to do with a possible urinary tract problem.  The cat will associate the discomfort with the litterbox, and in an effort to relieve the discomfort, they will go outside the box, for a more 'comfortable' location.  So, step one is to get a good check up to elimate the medical possiblity.  Sometimes, changing litter is not the best solution.  If there has never been a problem before, then it is unlikely changing litter would be necessary.  Try using the old type litter again.  Sometimes carpet powders are uncomfortable, as it can be breathed in and be harmful to lungs and sinuses.  The only way to thoroughly remove any residual smell or urine and/or feces, is to clean the area with an enzyme based product, like Nature's Miracle..Some of the 'rug cleaner rental' places also carry cleaners with enxymes.  This is the only effective way to remove any residue, thus discouraging the kitty  from using that area again.  Good luck with this kitty!  Thank you, again, for your time and inquiry.
Tomay