If you are trying to import a certificate into Personal Local Certificate store, and you face the situation that the “Enable strong private key protection. You will be prompted every time the private key is used by an application if you enable this option” option is grayed out as below picture.
You can follow the below instruction to resolve the issue:
a. Open the mmc.exe on run prompt
b. File add/Remove Snap-ins, double click on Group policy object:
c. Just finish and ok.
d. Open computer configuration> windows Settings> Security Settings> Local Policies>Security Options on the right panel. Then find System Cryptography: Force Strong key protection for user key stored on the computer and open it.
e. Select User is not required when keys are stored and used
f.
f. Apply and ok.
Adel N. Toosi's Blog 