Compatibility with Advanced Woo Search

I’ve got an ajax search plugin (Advanced Woo Search) on this site.

Having both that plugin and WpFC active at the same time gives a 500 error. Disabling either plugin solves the problem.

Is this a known issue? Is there a setting I should/should not be using?

Thanks

(By the way, I love your plugin and it works brilliantly on every other site)

The page I need help with: [log in to see the link]