@Gaiarsa I managed to fix this problem by deleting and re-inserting all content controls as plain-text (you can only utilise plain-text, combo and dropdown with this connector currently).
The document I am working on came from a 3rd party courier with a lot of content controls already inserted, we want to populate this document with data that we have in sharepoint etc.
Rather than manually removing and re-inserting all of the content controls, I wrote some vba to do it for me. Insert that into a module in the word vba editor and run it (F5), and you should no longer get this error. This obviously means the error was related to one or more of the content controls that were inserted (although I had already forced all to plain text before re-inserting and that didnt fix it).
Sub CleanseControls()
Dim existingControls As New Collection
Dim cc As ContentControl
Dim newcc As ContentControl
For Each cc In ActiveDocument.ContentControls
existingControls.Add cc
Next cc
For Each cc In existingControls
Dim tag As String: tag = cc.tag
Dim title As String: title = cc.title
cc.Range.Select
cc.Delete
Set newcc = ActiveDocument.ContentControls.Add(wdContentControlText)
newcc.title = title
newcc.tag = tag
Next cc
End Sub
