Cracks in emulsion on anaglypta

[Handypersonneedinghelp!]

Wondered if there's anyone out there who can help me. Please!
Am about to paint my son's bedroom. The walls have been painted (probably) quite a few times over a thick anaglypta. Bought the tester, applied a patch of paint, however upon drying, there are cracks in the colour. Applied another coat - still dried with cracks in the paint. What should I do? :?
Any/all answers appreciated. Thank you.