Web Part Error: File Not Found.

Error Details:
[TargetInvocationException: Exception has been thrown by the target of an invocation.]
  at System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean publicOnly, Boolean noCheck, Boolean& canBeCached, RuntimeMethodHandle& ctor, Boolean& bNeedSecurityCheck)
  at System.RuntimeType.CreateInstanceSlow(Boolean publicOnly, Boolean fillCache)
  at System.RuntimeType.CreateInstanceImpl(Boolean publicOnly, Boolean skipVisibilityChecks, Boolean fillCache)
  at System.Activator.CreateInstance(Type type, Boolean nonPublic)
  at System.Activator.CreateInstance(Type type)
  at Microsoft.SharePoint.WebPartPages.SPWebPartSerializer.get_DefaultControl()
  at Microsoft.SharePoint.WebPartPages.BinaryWebPartSerializer.SerializedWebPart..ctor(SPWebPartManager webPartManager, XmlNamespaceManager xmlnsManager, Byte[] sharedData, Byte[] userData, String[] links, Type type, SPWeb spWeb)
  at Microsoft.SharePoint.WebPartPages.BinaryWebPartSerializer.Deserialize(SPWebPartManager webPartManager, XmlNamespaceManager xmlnsManager, Byte[] userData, Byte[] sharedData, String[] links, Type type, SPWeb spWeb)
  at Microsoft.SharePoint.WebPartPages.SPWebPartManager.CreateWebPartsFromRowSetData(Boolean onlyInitializeClosedWebParts)

[FileNotFoundException: Could not load file or assembly 'System.Web.Silverlight, Version=2.0.5.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified.]
  at WilliamAdams.Rental.WebParts.Equipments..ctor()