How do I save in spotfire when the following error message is displayed?

Question

I've been rebuilding a broken tool in Spotfire but when I deleted all the old data, i now get an error when i tried to save. I've copied the error below. There is a lot of repeating script with the actual error about halfway down and at the bottom. I kept all the info below as I wasn't sure if it was helpful. Do I need to delete something or change a filter?

`Error message: Unable to save the file PcCatPlan V21 - DM.dxp.

SerializationException at Spotfire.Dxp.Framework:
The serialized (fragment of the) document contains non-owning references to document nodes that are not part of     (the fragment of) the document (details follow):
One of the references is to an object of type Spotfire.Dxp.Data.DataTable.
One of the references is to an object of type Spotfire.Dxp.Application.Filters.Filter.

One of the references is to an object of type Spotfire.Dxp.Application.Filters.FilterCollection.
One of the references is to an object of type Spotfire.Dxp.Data.DataTable.
One of the references is to an object of type Spotfire.Dxp.Data.DataColumn.
One of the references is to an object of type Spotfire.Dxp.Data.DataColumn.
One of the references is to an object of type Spotfire.Dxp.Data.DataColumn.
Object reference chain leading to the fault (closest reference first):

 (HRESULT: 8013150C)

Stack Trace:
   at Spotfire.Dxp.Framework.Persistence.Xml.SerializationFormatter.Serialize(Object graph)
   at Spotfire.Dxp.Framework.Persistence.PersistenceManager.SerializeForPersistence(Stream serializationStream,     Object graph, IServiceProvider serviceProvider, PersistenceVersionAttribute compatibilityVersion,     SerializationContext oldContext, SystemTypeSerializationSettings systemTypeSerializationSettings)
   at Spotfire.Dxp.Framework.Persistence.PersistenceManager.<>c__DisplayClass20_0.<Save>b__0()
   at Spotfire.Dxp.Framework.ApplicationModel.Progress.ExecuteSubtask(String title, ProgressOperation operation)
   at Spotfire.Dxp.Framework.Persistence.PersistenceManager.Save(DocumentTypes documentType, DocumentNode doc,     IDocumentSaveSettings settings, Stream targetStream)
   at Spotfire.Dxp.Framework.Persistence.PersistenceManager.SaveToTempFile(DocumentTypes documentType,     DocumentNode doc, IDocumentSaveSettings settings, Disposables cleanup, FileMetadata& fileMetadata)
   at Spotfire.Dxp.Framework.Persistence.PersistenceManager.Save(DocumentTypes documentType, DocumentNode doc,     IDocumentSaveSettings settings, String fileName)
   at Spotfire.Dxp.Framework.DocumentModel.DocumentManager`1.<>c__DisplayClass63_0.<Save>b__0()
   at Spotfire.Dxp.Framework.ApplicationModel.Progress.<>c__DisplayClass22_0.<Start>b__0()
   at Spotfire.Dxp.Framework.ApplicationModel.MonitorableProgress.Start[T](Func`1 action)
   at Spotfire.Dxp.Forms.Application.FormsProgressService.ProgressThread.DoOperationLoop()


InvalidOperationException at Spotfire.Dxp.Framework:
The serialized (fragment of the) document contains non-owning references to document nodes that are not part of         (the fragment of) the document (details follow):
One of the references is to an object of type Spotfire.Dxp.Data.DataTable.
One of the references is to an object of type Spotfire.Dxp.Application.Filters.Filter.

One of the references is to an object of type Spotfire.Dxp.Application.Filters.FilterCollection.
One of the references is to an object of type Spotfire.Dxp.Data.DataTable.
One of the references is to an object of type Spotfire.Dxp.Data.DataColumn.
One of the references is to an object of type Spotfire.Dxp.Data.DataColumn.
One of the references is to an object of type Spotfire.Dxp.Data.DataColumn. (HRESULT: 80131509)

Stack Trace:

at Spotfire.Dxp.Framework.Persistence.Xml.SerializationFormatter.Serialize(Object graph)`