Resolved. I think it was because I tried to open it when the doors were locked. Odd. Never had this issue before. Been a funny day. Probably the fantastic news on the Italian election. Well done Italy. Has the worm finally begun to turn. I also expect $60 dollar a barrel at some point. Are we finally returning to normality. In the words of Churchill, 'Now this is not the end. It is not even the beginning of the end. But it is, perhaps, the end of the beginning.'
PS - Thanks for the prompt and helpful replies, Henryge and ianhj.