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.BinaryWebPartSerializer.ByteArrayToObjectArray(Byte[] data)
  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)

[TypeLoadException: Could not load type 'Netcompany.COWI.Internet.ColorEnumerator' from assembly 'Netcompany.COWI.Internet, Version=1.0.0.0, Culture=neutral, PublicKeyToken=d51438346a13a100'.]
  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)