Error serializing derived Custom Collection Class

[big A]

I am receiving an error stating that File or Assembly name
<filname.dll> , or one of its dependencies, was not found

In one assembly I have three abstract classes

In another I have three derived classes from the abstract classes

The 1st class contains the 2nd class
The 2nd class is a custom collection for the 3rd class

when I serialize the 1st class I am receiving the error. The classes
look like the following:

Abstract classes:

using System;
using System.Xml.Seri alization;

namespace AbstractClasses
{
public abstract class ContainerBase
{
private LocationsCollec tionBase _locations = null;
public ContainerBase()
{
}

[XmlIgnore()]
public virtual LocationsCollec tionBase Locations
{
get
{
return this._locations ;
}
set
{
this._locations = value;
}
}
}
}
using System;
using System.Xml.Seri alization;

namespace AbstractClasses
{
public class LocationBase
{
public LocationBase()
{
}
}
}
using System;
using System.Collecti ons;
using System.Xml.Seri alization;

namespace AbstractClasses
{
public abstract class LocationsCollec tionBase : ICollection
{
private ArrayList _locationsColle ction;

public LocationsCollec tionBase()
{
this._locations Collection = new ArrayList();
}

public virtual int Add ( LocationBase Location)
{
return this._locations Collection.Add (Location);
}

[XmlIgnore()]
public virtual LocationBase this [int i]
{
get
{
return (LocationBase)t his._locationsC ollection[i];
}
set
{
this._locations Collection[i] = value;
}
}

#region ICollection Members
[XmlIgnore()]
public virtual bool IsSynchronized
{
get
{
return this._locations Collection.IsSy nchronized;
}
}

[XmlIgnore()]
public virtual int Count
{
get
{
return this._locations Collection.Coun t;
}
}

public virtual void CopyTo(Array array, int index)
{
this._locations Collection.Copy To(array,index) ;
}

[XmlIgnore()]
public virtual object SyncRoot
{
get
{
return this._locations Collection.Sync Root;
}
}

#endregion

#region IEnumerable Members

public virtual IEnumerator GetEnumerator()
{
// TODO: Add LocationsCollec tionBase.GetEnu merator implementation
return null;
}

#endregion
}
}
Derived classes:

using System;

namespace DerivedClasses
{
public class Container : AbstractClasses .ContainerBase
{
public Container()
{
base.Locations = new LocationsCollec tion();
}

public override AbstractClasses .LocationsColle ctionBase Locations
{
get
{
return base.Locations;
}
set
{
base.Locations = value;
}
}

}
}
using System;

namespace DerivedClasses
{
public class Location : AbstractClasses .LocationBase
{
public Location()
{
}

public virtual string LocationName
{
get
{
//return base.LocationNa me;
return "Location: " + DateTime.Now.To String();
}
}
}
}

The code to serialize looks like:

StreamWriter writer = new
StreamWriter(@" C:\windows\temp \serializetest\ Container1.xml" );
DerivedClasses. Container Container1 = new DerivedClasses. Container();
XmlSerializer serializer1 = new
XmlSerializer(t ypeof(DerivedCl asses.Container ));
serializer1.Ser ialize(writer.B aseStream,Conta iner1);
Does anybody know what is wrong?

thanks,
-a.n.