Bizarre 404 errors from Google AdWords

Hi folks, 

Just had a look at Google Analytics' exit pages for a site we manage and found dozens of 404 errors, for which the source is claiming to be Google CPC. There is a live AdWords account but all landing pages, widgets and links have been checked on all pages and there's no issues. The website in question does link off to a third party site where the user can complete a transaction/booking. Have done a full crawl and site audit on Raven, which found no major issues or 404 errors. 

Any idea what could be generating these 404 errors and how we can overcome them? Could they coming from the third party site? Here's an example of just a few of the errors...