To generate a MachineKey in IIS, follow the steps below. For admins without access to IIS, your host can often assist with generating MachineKeys and there are third-party websites online that can generate them as well. NOTE: Earlier versions of IIS may look different from the images below. There are directions on this site for doing this in earlier versions.
1 - Open IIS, and select the site you want to generate a key for in the list of sites:
2 - In the right-hand panel, double-click the Machine Key icon:
3 - Change the validation method dropdown to HMACSHA256 and uncheck the two boxes:
4 - You should now see a Generate Keys link to the far upper right:
5 - Click that link, and copy the value from the first text box - that is your new MachineKey. Note that for some purposes, you may have to generate multiple keys.
NOTE: When you are done generating keys and close the window, you may be prompted if you want to save the changes. Be sure to click no!