You need to give a lot more detail for anyone to be able to help.
1. What version of ADS are you using?
Resp: ADS2013
2. What type of model have you using from the vendor?
Reso: CREE CGH40010
3. How have you 'added the model'?
Based on the following instruction given by the vendor:
ADS Installation Notes for Cree GaN HEMT Large Signal Models
This instruction sheet covers the installation in ADS for Cree’s CGH40006P, CGH40006S, CGH40010F, CGH40010P, CGH40025F, CGH40025P, CGH40035F, CGH40045F, CGH40090PP, CGH40120F and CGH40180PP GaN HEMT models.
1. Remove “ADS_”.
2. **Important** Save the .zip file to disk.
3. Start up ADS and look for the drop-down menu in main window titled "DesignKit."
4. Choose the option "Install Design Kits." (Note: A window will pop up with Steps).
5. Use ADS step 2 "Define Design Kit" and browse to the kit file.
6. At the bottom of this ADS window you can select user level, project level, etc.
Then click OK.
Note: This will install the kit.
7. Open a design window and select model from the palette.
Note: Here you can pick and place the models.
8. The Gate voltage is -3.0 < Vg < -1.5, with pinch off ~2.9 Volts. Vd is valid
from ~28V to ~48V
Thank you so much for your quick response