Roomba keeps saying clean brushes yet are clean!

Question

Bought Roomba 560 for Xmas present. Using it for first time - it keeps stopping during cleaning and says "please remove and clean brushes", yet, brushes are clean!! keeps doing this approx every 10 minutes. I have another Roomba 560 which does not do this and works perfectly on the same carpet without stopping and asking for brushes to be cleaned. Please help!!!