Could be its using a wrong VDJ folder, VDj has several locations it can use and Lexicon is sometimes confused which is the right one.
You can check lexicon logs (Lexicon database & log locations) and it will say where it is looking for your VirtualDJ folder. Compare that with the correct folder which you can see by opening VDJ, settings, then clicking the very small settings icon in the bottom (should open the VirtualDJ folder).