Can't load any membership providers

Hello,

I have just loaded an Alloy example site and was starting to look at logging into episerver. However, when I checked the <membership> and <roleManager> sections in web.config, they were empty. 

So after checking the docs at https://world.episerver.com/documentation/developer-guides/CMS/security/Authentication-and-authorization/, I filled out this section with the following config:

<membership defaultProvider="WindowsMembershipProvider"
userIsOnlineTimeWindow="10"><providers><clear /><add name="WindowsMembershipProvider"
type="EPiServer.Security.WindowsMembershipProvider, EPiServer"
deletePrefix="BUILTIN\" /></providers></membership><roleManager enabled="true" defaultProvider="WindowsRoleProvider"><providers><clear /><add name="WindowsRoleProvider"
applicationName="EPiServerSample"
type="EPiServer.Security.WindowsRoleProvider, EPiServer" /></providers></roleManager>

However, when I load the site now I get the following error message displayed:

Parser Error Message: Could not load type 'EPiServer.Security.WindowsRoleProvider' from assembly 'EPiServer'.

Does anyone know why this might be happening? As I'm using configuration straight out the latest docs I would have thought this would work..

Thanks,

Sam