URL Access Scripting problem

Hello,
I have a problem with this script

set newFile to (path to desktop as text) & "npinstal.exe"
tell application "URL Access Scripting"
activate
download "ftp://user:password@site.domain.xx/npinstall.exe" to
newFile with progress and autentication
display dialog result
quit
end tell

when i run it show this error

tell current application
path to desktop as text
"Macintosh HD:Users:cdo_panu:Desktop:"
end tell
tell application "URL Access Scripting"
activate
«data
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»
"URL Access Scripting ha trovato un errore: Errore nelle estensioni"

The english translation of the error is
URL Access Scripting found a error: Extension error.
My system is OSX 10.4.11
and URL Access Scripting version is 1.1
Whith http download it works.
When i use unavaliable user name or wrong password it work and say
that cannot autenticate.
Thanks all.

Alberto