[Plugin: SEO Ultimate] Category pages produce 404 error when removing URL bases

When using the ‘Remove the URL bases of Categories’ feature, I find my Category pages produce a 404 error

Permalinks are configured with a custom structure of: /%postname%/

Any idea how I can fix this? I don’t really want to have the ‘Category’ as part of my URL structure.

Thanks

https://www.ads-software.com/extend/plugins/seo-ultimate/