Call an Enity Framework method from Revit add-in causes NotSupportedException

Question

I created an ADO.NET Entity Data Model using Entity Framework code-first in a RevitAddin project.

public static  class ElevationDao
{
    public static int GetId(int length)
    {
        var db = new DbContext();

        var obj = db.Elevations.Where(x => x.Value == length);

        if (obj.Count() == 0) 
           throw new Exception();

        return obj.First().ID;
    }
}

And I call this function in Execute method of Revit command:

[Transaction(TransactionMode.Manual)]
public class Class1 : IExternalCommand
{
    public Result Execute(ExternalCommandData commandData, ref string message, ElementSet elements)
    {
        int id = ElevationDao.GetId(3300);
        return Result.Succeeded;
    }
}

When I execute this command, Revit throws a NotSupportException and automatically shuts down its session.

Can anyone explain this and give me a hint? Thank you.

PS: It only happens on my laptop, On my company's computer, it works fine.