Error Serializing Observable Collection Windows Store

Error Serializing Observable Collection Windows Store

I have an observable collection I am trying to serialize to disk. The
error that is received is :
Type 'VisuallySpeaking.Data.GrammarList' with data contract name
'GrammarList:http://schemas.datacontract.org/2004/07/VisuallySpeaking.Data'
is not expected. Consider using a DataContractResolver or add any types
not known statically to the list of known types - for example, by using
the KnownTypeAttribute attribute or by adding them to the list of known
types passed to DataContractSerializer."} System.Exception
{System.Runtime.Serialization.SerializationException}
Here is my data object:
namespace VisuallySpeaking.Data
{
[CollectionDataContract]
public class GrammarList : ObservableCollection<GrammarDataObject>
{
public GrammarList() : base()
{
Add(new GrammarDataObject("My Name", "My name
is","Assets/SampleAssets/MyName.png"));
Add(new GrammarDataObject("Where is", "Where is",""));
Add(new GrammarDataObject("Dog", "I have a
dog","/Assets/SampleAssets/westie.jpg"));
}
}
[DataContract]
public class GrammarDataObject : VisuallySpeaking.Common.BindableBase
{
private string _Name;
private string _SpeakingText;
private string _ImagePath;
public GrammarDataObject(string Name, string SpeakingText, string
ImagePath)
{
this.Name = Name;
this.SpeakingText = SpeakingText;
this.ImagePath = ImagePath;
}
[DataMember]
public string Name
{
get { return _Name; }
set
{
if (this._Name != value)
{
this._Name = value;
this.OnPropertyChanged("Name");
}
}
}
[DataMember]
public string SpeakingText
{
get { return _SpeakingText; }
set
{
if (this._SpeakingText != value)
{
this._SpeakingText = value;
this.OnPropertyChanged("SpeakingText");
}
}
}
[DataMember]
public string ImagePath
{
get { return _ImagePath; }
set
{
if (this._ImagePath != value)
{
this._ImagePath = value;
this.OnPropertyChanged("ImagePath");
}
}
}
}
I assume that I have somehow marked my GrammarList class incorrectly, but
it escapes me as to how to resolve.
Thanks!