Allen, thank you for replying.  My code doesn't involve any recalculations,
but I think your answer must point to the problem.  As you say, there must be
something in my code where Access is "catching up" in break mode.  Here is an
overview of my code (and this has to do with writing letters):

' One form1, there is a command button that you click to open form2

Private Sub Command_Click()
   DoCmd.OpenForm "form2", , , , acFormAdd, acDialog, newdata
           Response = acDataErrAdded
   Sub AddToListOfRecentLetters
End Sub

'form2 has several listboxes of return addresses
'names of addresses, and
'a textbox where you give the letter a name for saving
'there is a command button on form2 Captioned "WRITE LETTER"
'clicking this button opens Word by Automation and fills in Bookmarks
'with information from the listboxes.
'As to the name you are giving the letter (to prevent duplicate names)
'there is a local table containing a counter.  A sub routine picks up the
'number in the table, adds that number at the end of the name, and increments
'the table by one. (I use a Long variable type for this)
'Access "knows" there is a Word Document open because of a
"While ... Wend loops that keeks looping as long as the Document Exists
'when the Word Document is closed, the Document
'no longer exists and this kicks you out of the While ... Wend
'to close form2

    On Error GoTo CloseForm2
    While objWord.IsObjectValid(objWdDoc)
    Wend
    CloseForm2:
    DoCmd.Close

'You are now back to form1, and the next line of form1
'calls a sub routine in the module
'(Sub AddToListOfRecentLetters) that inserts basic information
'about the letter (Addressee, File Name, Date of Letter)
'into a local table

   Set rst = New ADODB.Recordset
   With rst
       .CursorLocation = adUseClient
       .CursorType = adOpenKeyset  ' page 254,256 of Dev. Handbook
       .LockType = adLockOptimistic    ' page 256
       .Open "RecentLetters", CurrentProject.Connection
       .addnew
           !clientID = lngclientID
           !LetterFileName = strWdDocName & "_" & cstr(lngDocumentID)
        .Update
   End With
   rst.Close

The bug occurs where you try to add strWdDocName to the table, and the error
message says there is a type mismatch because strWdDocName is Null.  This
variable is not null.  When the letter was saved by Word automation, it saved
properly under this name.  Somehow, this variable has been "wiped out."

So thinking along the lines of your suggestion, is there a problem with the
DoCmd.Close command happening too fast, or is there some problem getting the
document ID number out of the local table, and why would that be?  It is as
if there is some subtle error that has occurred in an earlier line of the
code that finally triggers the crash on what should be an innocuous line of
code.