Role Manager feature has not been enabled (Identity)

Hello,

I'm using webforms and I'm trying to add users to roles using the following code:

Roles.AddUserToRole(userTxt.Text, roleTxt.Text);

At first, I was getting the message "The Role Manager feature has not been enabled."

So, I added these lines to web.config of the Admin role

"1.0"?>
enabled="true"
cacheRolesInCookie="true" >
"Administrator"/>
"*"/>

Now, I get this parser error message "Parser Error Message: It is an error to use a section registered as allowDefinition='MachineToApplication' beyond application level. This error can be caused by a virtual directory not being configured as an application in IIS."

I would appreciate any kind of help, thank you in advance.