Brilliant thank you - that fixed it.
I don't what fixed the previous issue - I came in to work the next day and didn't get the error.
When I reinstalled the extensions I did install the latest version of the MySQLi server behaviours. It all seems to work.
The only thing I have now (that I didn't have before) is that where I have used SESSION variables from the User Authentication > MySQLi Log In User, to show regions I have red exclamation marks in the Server Behaviors panel. I have attached an example. I have found that if I remove the comment code // Begin Show Region the exclamation mark disappears from the Server Behaviour panel but so does the whole behavior row. It's not a major issue as I can remove that bit of code but I have A LOT of these throughout my sites