Tag search & replace with command line

Hi,

Can anyone see my error below? I think it fails in the following lines

if tag.value= OldValue then
tag.value= NewValue

I want to run the macro like this

macro tagreplace abc xyz

The majority of the code I copied from an earlier post on this group.
Any suggestions?

using V7

' tagreplace.bas
'
' ===================================================================
Const ENDofFILE% = -1
Const STARTofFILE% = 0

Sub main
Dim tag as New MBEtag
Dim element as New MBEelement
Dim tagelement as New MBEelement
Dim filepos as Long
Dim OldValue as String
Dim NewValue as String
Dim cmd As String
' parse command line

cmd= Command$

OldValue = (word$(cmd,1)) 'gets the old value
NewValue = (word$(cmd,2)) 'gets the new value

elcounter = 0%
filePos = element.fromFile(STARTofFILE)

While filePos <> ENDofFILE

'if an element has a tag attached, then retrieve it.
if element.getMbeTag(tag)=MBE_success then

if tag.value= OldValue then
tag.value= NewValue

'get the underlying tag element
stat=tag.getMBEelement(tagelement)

'so we can rewrite it with it's new value
stat=tagelement.rewrite()

end if

end if
filePos = element.fromFile(filePos + element.fileSize)
Wend
END SUB