C# - Remove An Item From A Collection (MembershipUserCollection) - Enumeration Operation May Not Execute

I use asp.net 4, ef 4 in c#.I use System.Web.Security to manage users in my web application.

I have a collection of users in MembershipUserCollection and I need remove some users during a foreach on that collector.

I suppose it is impossible to remove an item from the collector when you are looping.

MembershipUserCollection users = Membership.GetAllUsers();
foreach (MembershipUser x in users)
{
if (!Roles.IsUserInRole(x.UserName, "CMS-AUTHOR"))
{
users.Remove(x.UserName);
}
}

Error: Collection was modified; enumeration operation may not execute.