New category redirecting to broken page

I had a category called ‘competitions’. This has now been renamed to ‘My Competition Entries’. However there was a page by the same name, so I changed both the name and the slug of that page to something completely different (old-comp-entries-old) but whenever I try to go to http://www.myblog.com/category/my-competition-entries it redirects to a 404 error, changing the address back to a page that no longer exists.

I have WP No Category Base plugin stripping the category name. When I disable this it includes the blog/ prefix (I’m running multisite) and I can see the category home page.

I have tried updating permalinks and deleting cache but WordPress no longer recognises the category. It’s frustrating as hell and I’m guessing there’s a simple solution to this, but what is it?

Any pointers gratefully received.