I upgraded the CKeditor version to 3.66 which seems to have resolved the problem, however despite following the instructions on the CKEditor website (as suggested on this forum) there was an error due to the gallery folder not being in the plugins directory in the 3.6.6 build.
I have copied the gallery folder from the previous install which seems to have helped, but I was wondering if someone could confirm the updgrade instruction for this.
I am now getting an error;
Uncaught TypeError: Cannot read property 'length' of null ckeditor.js:88
(anonymous function) ckeditor.js:88
(anonymous function) ckeditor.js:125
(anonymous function) ckeditor.js:24
(anonymous function) ckeditor.js:23