I'm using the latest version of IMatch 2017. I am doing a database diagnosis to hopefully weed out problems, but right now, if I drag any category to the category builder, I'm getting an "unknown prefix" error, with error code 15006. This is regardless of whether the category is by itself/has child nodes.
This is related to the already fixed bug 'Category Formula Parser' (for next release): https://www.photools.com/release-notes/