The Oxford Nexus email, calendaring, address book (etc.) service is built upon Microsoft Exchange. One of the mechanisms to keep your data secure when you are using the service is to use server certificates that your client software should recognise and trust.
From time to time these certificates must be renewed. However, JANET, the UK's education and research network is now issuing a different type of certificate to that which we had before. This change will not be noticed by most people. However, some software may alert you to the change.
From 7 am on Tuesday 8 May 2012, any software or device that you are using may
notice a security change
You may be prompted to re-start your software. Please do so, and the prompt should disappear. If you are using a hand held device (e.g. smart phone), you should re-start it if any prompts or error messages are seen.