I have had to deactivate and delete the plugin. The plugin or a conflict with plugin was causing problems within the Admin area. i.e. I could not access any posts, pages, comments etc (the admin panel was showing I had not posts, pages or comments), using the admin was very slow.
However, now that I have deleted the plugin I am still getting a MapPress error message, see below…
The plugin mappress-google-maps-for-wordpress/mappress.php has been deactivated due to an error: Plugin file does not exist.
The plugin has been deleted. Has an entry been left in the database?