The Role Manager feature has not been enabled

Solution 1:

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

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