'The RPC server is unavailable.' when looping through word documents

Question

I am working on a utility to find and update DOC VARIABLES in Word. I have a section of code to loop through the documents and present a Message Box with the variable name, but I'm receiving an error when it tries to open the next document. The error is:

System.Runtime.InteropServices.COMException: 'The RPC server is unavailable. (Exception from HRESULT: 0x800706BA)

I'm confused because my code does not access any network. I think what might be happening is the Word is closing when the document closes, but I cannot find a solution to prevent that.

Other things I've tried:

1. Confirmed UAC is Disabled
2. Confirmed RPC Services are Running

3. Confirmed Registry Values for RPC and DCOM are correct

   Private Sub LoopTemp()
       Dim oDir As New DirectoryInfo(dPath)
       Dim oFileArr As FileInfo() = oDir.GetFiles()
       Dim oFile As FileInfo
       Dim oVar As Variable
       Dim oDoc = New Document()
   
       Dim oWord As Application
       oWord = CreateObject("Word.Application")
       oWord.Visible = False
   
       For Each oFile In oFileArr
          oDoc = oWord.Documents.Open(oFile.FullName)
   
          For Each oVar In oDoc.Variables
              MsgBox(oVar.Name)
          Next
   
          oDoc.Close(SaveChanges:=WdSaveOptions.wdSaveChanges)
   
       Next
       oWord.Quit()
   End Sub
   

Answer 1

The RPC error appears when a "pointer" to a COM object is not correctly released from memory before code tries to re-use it. This is a common enough problem when automating Office applications from outside the application, itself. Especially when working from .NET great care must be used.

Another very important thing to note is that the New keyword should never be used with any Office object except Application. Although the APIs allow it, never use New Document with Word as this creates a Document object that can't be correctly released.

For reasons of efficiency, starting the Word application once should be sufficient - it's not necessary to repeat that within a loop, as long as the COM objects it uses are correctly released (set to Nothing and garbage collected).

I would write the code in the question as follows:

Private Sub LoopTemp()
    Dim oDir As New DirectoryInfo(dPath)
    Dim oFileArr As FileInfo() = oDir.GetFiles()
    Dim oFile As FileInfo
    Dim oVar As Variable = Nothing
    Dim oWord As Application = NOthing
    Dim oDoc As Document = Nothing

    oWord = New Word.Application
    oWord.Visible = False

    For Each oFile In oFileArr
        oDoc = oWord.Documents.Open(oFile.FullName)
        For Each oVar In oDoc.Variables
            MsgBox(oVar.Name)
        Next
        oVar = Nothing
        oDoc.Close(SaveChanges:=WdSaveOptions.wdSaveChanges)
        oDoc = Nothing

        GC.Collect()
        GC.WaitForPendingFinalizers()
        GC.Collect()
        GC.WaitForPendingFinalizers() 
    Next

    oWord.Quit()
    oWord = Nothing
    GC.Collect()
    GC.WaitForPendingFinalizers()
    GC.Collect()
    GC.WaitForPendingFinalizers()

End Sub