I have had so many problems with this that I have given up. But today I have gathered enough energy to have another wander around the internet and hey presto!!
Of course I changed two things so I don't know which of these it is or both.
Uncheck the stay signed in box when you sign in.
Go to tools, internet options, privacy, advanced privacy and uncheck the box that says that you filter out third party cookies.
And this time it works. I am not optimistic enough to think that it will next time but who knows :-)