Thanks
1. The message in the top left corner has always been there since I upgraded and is also there with all three other sites. It’s there with Firefox and Safari
2. All sites have a different theme but have the same problem so I don’t think it is a theme issue so will try the plugin reset – all sights have a couple of plugins in common so it would seem most likely
I was about to reset the plugins as suggested but tried to login to the sites once again Login is now working again on all the sites. Not sure what happened or where the problem lay but I am able to access the admin dashboard again.
Thanks for your help and I shall now upgrade to 3.5.1