Is the tblPersoon implementing IEnumerable<T>? You may need to do it using:
var query = (from p in tblPersoon.Cast<Person>() select p).Single();
This kind of error (Could not find an implementation of the query pattern) usually occurs when:
using System.Linq)IEnumerable<T>Edit:
Apart from fact you query type (tblPersoon) instead of property tblPersoons, you also need an context instance (class that defines tblPersoons property), like this:
public tblPersoon GetPersoonByID(string id)
{
var context = new DataClasses1DataContext();
var query = context.tblPersoons.Where(p => p.id == id).Single();
// ...