Could not find an implementation of the query pattern

You may need to add a using statement to the file. The default Silverlight class template doesn't include it:

using System.Linq;

You must have forgotten to add a using statement to the file like this:

using System.Linq;

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:

• You are missing LINQ namespace usage (using System.Linq)
• Type you are querying does not implement 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();
    // ...

Make sure these references are included:

• System.Data.Linq
• System.Data.Entity

Then add the using statement

using System.Linq;