I can't erase authorisation on my Mac. I had to install 4.5 because I have brought a new Kobo reader but cannot get it connected/authorised. I have changed my email address and the computer authorisation is under old address. I tried to erase authorisation but keep getting the message "unable to erase authorisation. Please try after some time." Have been trying for 4 days now. I cannot get my Kobo to authorise either and this is possibly because of the computer authorisation. I am getting fed up and very frustrated, it's not user friendly. I have a brand new Kobo and can't load any library books. Desperate for help.