If you'd like to attach your input file, I'd be happy to take a look. You could also do a quick forum search here on "missing loc" and find a possible solution. It's historically been one of the most uninformative (if not misleading) error messages DirectRT has come up with.

Gist of the other posts is that it's usually it's a syntax problem in the previous trial (or the line *before* the line indicated by DirectRT's error message. It because that syntax throws off how DirectRT reads in the input and so it thinks something like a LOC value or a Style ID is missing.