I'm trying to replace a mergeField in a writer document header using
insertString. The code throws a RuntimeException.

Here's some example code:

#!/usr/bin/python

import sys
import uno
from os import getcwd
from unohelper import Base, systemPathToFileUrl, absolutize
from com.sun.star.beans import PropertyValue, UnknownPropertyException
from com.sun.star.uno import Exception as UnoException, RuntimeException

localContext = uno.getComponentContext()
resolver =
localContext.ServiceManager.createInstanceWithContext("com.sun.star.bridge.UnoUrlResolver",
localContext )
ctx = resolver.resolve(
"uno:socket,host=localhost,port=8100;urp;StarOffice.ComponentContext" )
smgr = ctx.ServiceManager
desktop = smgr.createInstanceWithContext("com.sun.star.frame.Desktop", ctx )

inProps = PropertyValue( "Hidden" , 0 , True, 0 ),
fileUrl = absolutize(systemPathToFileUrl( getcwd() ) ,"letter1.ott")
doc = desktop.loadComponentFromURL( fileUrl , "_blank", 0, inProps )

fields = doc.getTextFields().createEnumeration()
while fields.hasMoreElements():
        field = fields.nextElement()
        fieldname = field.getPresentation(0)

        try:
                isDatabaseField = field.getPropertyValue("DataBaseFormat")
        except UnknownPropertyException :
                isDatabaseField = False

        if isDatabaseField:
                try:
                        doc.Text.insertString(field.getAnchor(),"New value for "
+ fieldname,1)
                except RuntimeException, e:
                        print "RuntimeException while to replacing field: " +
e.Message 

Each time i try to replace a databasefield in the header (field created using a
ooo calc spreadsheet), the program throws a runtimeexception. 

I've tried it using java and python, both have the same problem.