The Role Manager feature has not been enabled

I found 2 suggestions elsewhere via Google that suggested a) making sure your db connectionstring (the one that Roles is using) is correct and that the key to it is spelled correctly, and b) that the Enabled flag on RoleManager is set to true. Hope one of those helps. It did for me.

Did you try checking Roles.Enabled? Also, you can check Roles.Providers to see how many providers are available and you can check the Roles.Provider for the default provider. If it is null then there isn't one.

If you got here because you're using the new ASP.NET Identity UserManager, what you're actually looking for is the RoleManager:

var roleManager = new RoleManager<IdentityRole>(new RoleStore<IdentityRole>(new ApplicationDbContext()));

roleManager will give you access to see if the role exists, create, etc, plus it is created for the UserManager

You can do this by reading from the boolean property at:

System.Web.Security.Roles.Enabled

This is a direct read from the enabled attribute of the roleManager element in the web.config:

<configuration>
  <system.web>
    <roleManager enabled="true" />
  </system.web>
</configuration>

Update:
For more information, check out this MSDN sample: https://msdn.microsoft.com/en-us/library/aa354509(v=vs.110).aspx