Does your "C:\Users\YOUR_USERNAME\Documents\Image-Line\Data\GMS" folder contain any GMS presets?
If not, can you try the following:
- Navigate to "C:\Program Files (x86)\Image-Line\FL Studio 11\Plugins\Fruity\Generators\GMS\Synth Programs"
- Copy the folders in this location.
- Now navigate to "C:\Users\YOUR_USERNAME\Documents\Image-Line\Data\GMS"
- Paste the previously copied folders into this location.
Relaunch FL Studio and check if your GMS presets are present within the plugin.