There are some SynthMaker FL Generators that have been uploaded that won't load and it seems that the problem is simply in the naming of the folder.
example: X12FL.dll must be in a folder named X12FL and this must be placed in C:\Program Files\Image-Line\FL Studio\Plugins\Fruity\Generators.
then Refresh and the .dll should show in Fruity generator plugins and then it will load straight into SynthMaker when selected.