I don't know if the product is auto or manual install, but you need to make sure it's in the correct folder on your PC. Mixcraft settings will show you where Mixcraft will be looking for those plugins. You can also add more folders to the list it need be. 32 bit and 64 bit plugins will typically be placed in their respective folders. Make sure it's in the correct folder first and then if Mixcraft is open, close it and re-open so that Mixcraft can scan the plugin. You can also rescan through settings but that usually takes longer.
Mixcraft 8 Pro Studio 64-Bit
Windows 10 64-Bit AMD Athlon II X4 645 3.1 GHz 10GB Ram 7200RPM HDD
Behringer UMC404HD v4.38 interface
Audio Technica AT2010 Condenser and Dynamic Mics
Fender Squier VM70s Jazz Bass Active Pre-amp.