Runtime error 5941 when clicking requirwed field contaning text

I have a form document with several fields which are required before the document can be saved. Variable is defined as follows:

Option Explicit
Dim sInFld As String
Private WithEvents wdApp As Word.Application

The following code is called on the save as event for all required fields.

Sub MandatoryDOCTITLE()
If ActiveDocument.FormFields("DOCTITLE").Result = "" Then
Do
sInFld = InputBox("Please enter the Document Title.")
Loop While sInFld = ""
ActiveDocument.FormFields("DOCTITLE").Result = sInFld
End If
End Sub

Runtime error 5941 occurs whenever I click on a form field bearing this code that contains text. The code executes properly and the file is saved, but the runtime error is distracting and a nuisance. Is there a reliable way to prevent it?