 <p>We managed to find a solution so I'm going to respond to myself just in case someone else has the same problem and is looking for a fix. </p> <p>We created a new page and started copying the code from the page across. We would publish the website after we added some code and tested that we could browse to the page, which we could. Eventually we had all the code in the new page and it was working fine. Problem solved! </p> <p>Out of interest we renamed the new page to the old one and tried to access the page and we got the same error again. On changing the name back it worked fine.</p> <p>TLDR version</p> <ol> <li>Create a new page with a different name, copy your code across.</li> <li>Try renaming the page.</li> </ol>