LINQ & Entity Framework - List.Contains doesn't work

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C#

MVC4

entity-framework

I'm trying to filter data with LINQ and Entity Framework 6 in MVC 4 WebAPI with .NET 4.

The issue is over here:

public object Get(int id)
    {
        SiscalContext sys = new SiscalContext();
        if (!sys.FileExist(id))
            throw new Exceptions.BadRequest.FIDNoExist();
        User LoggedUser = sys.AuthUserInfo();
        File file = sys.Files.Where(itm => itm.ID == id).FirstOrDefault();
        if (file.Owner != LoggedUser.ID && (file.Permissions == Permissions.OnlyMe || (file.Permissions == Permissions.Specific && !file.Group.Contains(LoggedUser.ID))))
            throw new Exceptions.Forbidden.NotAllowed();
        return file;
    }

Specifically in:

!file.Group.Contains(LoggedUser.ID)

When this is excecuted the next error appears:

The specified type member 'Group' is not supported in LINQ to Entities. Only initializers, entity members, and entity navigation properties are supported.

The model of File is the next:

public enum Permissions { OnlyMe, Specific, Public };
public enum FileType { Folder, File };

public class File
{
    public int ID { get; set; }
    public string Name { get; set; }
    public int Directory { get; set; }
    public int Owner { get; set; }
    public Permissions Permissions { get; set; }
    public virtual List<int> Group
    {
        get
        { return string.IsNullOrEmpty(this.GroupJSON) ? new List<int>() : JsonConvert.DeserializeObject<List<int>>(this.GroupJSON); }
        set
        { GroupJSON = JsonConvert.SerializeObject(value); }
    }
    [JsonIgnore]
    public string GroupJSON { get; private set; }
    public FileType Type { get; set; }
}

What I can do to keep using the same model?