I was trying to create a strong name for an assembly in Visual Studio from the project properties using the dialog:

After clicking OK I received the following error message: The operation could not be completed. Access is denied.

I then tried from the command prompt using sn.exe and received the same type of message: Failed to generate a strong name key pair -- Access is denied.

I found the following blog post Create Strong Name Key - Access Denied Error, but it applies to Windows XP. I searched around for a RSA\MachineKeys folder and found three different locations but it seems the folder C:\ProgramData\Microsoft\Crypto\RSA\MachineKeys is the magic place.

I gave my user the following permissions on the MachineKeys folder and then I was able to sign my assembly

When I changed the permissions on the folder it complained I could not change permissions on the files in the folder, so I cancelled out of the application of the file permissions. It looks like I’d have to take ownership of the existing files in order to change their permissions which I decided not to do at this point.

I hope this helps