"My World" is corrupted and cant be started

Issue has only recently arisen, MCPE has until now been running OK since installed in May. Minecraft starts but then when you try to open or start a new world you get the message "my world" is corrupted cant be started. Have tried fix suggested on forum which was to delete the folder with the worlds in, uninstall and reinstall. Didnt work. Have tried opening different types of worlds (infinite, flat etc) but get same message.

PS - OK I posted in the wrong project. Cant see how to log a PE specific bug ?