Thanks Oldscribe. I found that the the fault lay with either the keyboard or mouse. I went to System Preferences/Bluetooth/advanced and then disabled "Allow Bluetooth to wake this computer". I now wake it from sleep using the "on" button on the back of the screen and all is well.
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments. After that, you can post your question and our members will help you out.