IUniqueValueRenderer.AddReferenceValue Causes program to exit with error

I am using the IUniqueValueRenderer.AddReferenceValue statement in a program to add additional values to an existing value for symbology purposes. After the value has been added, I perform a IUniqueValueRenderer.ReferenceValue statement to check the values. It does not show the new value as having been added although the statement executes without error. I can do several statements afterwords that will work just fine, until I do a ZoomToWhole on the page. At which point, the program sends an error:

System.AccessViolationException: Attempted to read or write protected memory.

If I remove this part of the program, don't add reference values, the program runs fine without error. I am able to add values to the renderer and continue on. As long as the AddReferenceValue statement is commented out, the rest of the program works. Here is the code:

For i = 0 To pRender.ValueCount - 1
pRender.AddReferenceValue(pRow.Value(ndx), "UNCOMMITTED")
pMXDoc.CurrentContentsView.Refresh(pLayer)
pMXDoc.UpdateContents()
pApp.SaveDocument()
System.Runtime.InteropServices.Marshal.FinalReleaseComObject(pRender)
pRender = gLayer.Renderer
pMXDoc.PageLayout.ZoomToWhole()
Next i

As you can see from the code, I have tried all kinds of things to free whatever memory it perceives as being in use.