Q:

SUPER SIMPLE LINQ to filter row does not work

Spent about 4 hours trying to figure this out without success. 
IQueryable<userTOM> Infolist =  userTOMs();
        var rbtUserId = Infolist.Where(x => x.UserName == FormsUserName);

userTOMs <-- Does not exist. 
Remade the namespace many times but will not appear. 

A:

IQueryable does not run immediately on the database. In order to run the query, one has to run functions such as .ToList(), or .Count() on the IQueryable.
Therefore, nothing in your pasted code triggers the database request, and the ID will not be retrieved. I would modify your request to this:
IQueryable<userTOM> Infolist =  userTOMs();
userTOM rbtUser = Infolist.FirstOrDefault(x => x.UserName == FormsUserName);

Guid rbtUserId; //assuming this will be populated with a Guid value
if (rbtUser != null) {
    rbtUserId = rbtUser.Id; //assuming "ID" is the property name
}

