Web Part Error: An error has occurred.

Error Details:
[ArgumentException: The serialized data is invalid.]
  at System.Web.UI.ObjectStateFormatter.Deserialize(Stream inputStream)
  at Microsoft.SharePoint.WebPartPages.Utility.DeserializeByteArrayToObject(Byte[] bytes)
  at Microsoft.SharePoint.WebPartPages.BinaryWebPartDeserializer.LoadInitialWebPart()
  at Microsoft.SharePoint.WebPartPages.BinaryWebPartDeserializer.Deserialize()
  at Microsoft.SharePoint.WebPartPages.SPWebPartManager.CreateWebPartsFromRowSetData(Boolean onlyInitializeClosedWebParts)

[TypeLoadException: Could not load type 'SilverIT.SPRating.PictureGalleryWebPart.PictureGalleryWebPart+RateType' from assembly 'SilverIT.SPRating, Version=1.0.0.0, Culture=neutral, PublicKeyToken=01216df7de0ed5f9'.]
  at System.RuntimeTypeHandle._GetTypeByName(String name, Boolean throwOnError, Boolean ignoreCase, Boolean reflectionOnly, StackCrawlMark& stackMark, Boolean loadTypeFromPartialName)
  at System.RuntimeTypeHandle.GetTypeByName(String name, Boolean throwOnError, Boolean ignoreCase, Boolean reflectionOnly, StackCrawlMark& stackMark)
  at System.RuntimeType.PrivateGetType(String typeName, Boolean throwOnError, Boolean ignoreCase, Boolean reflectionOnly, StackCrawlMark& stackMark)
  at System.Type.GetType(String typeName, Boolean throwOnError)
  at System.Web.UI.ObjectStateFormatter.DeserializeType(SerializerBinaryReader reader)
  at System.Web.UI.ObjectStateFormatter.DeserializeValue(SerializerBinaryReader reader)
  at System.Web.UI.ObjectStateFormatter.DeserializeValue(SerializerBinaryReader reader)
  at System.Web.UI.ObjectStateFormatter.Deserialize(Stream inputStream)