Automator Rename Finder Items NOT working in Leopard

try
tell application "Finder" to set the source_folder to (folder of the front window) as alias
on error -- no open folder windows
set the source_folder to path to desktop folder as alias
end try

repeat
display dialog "Find and Replace:" default answer "" buttons {"Cancel", "OK"} default button 2
set the search_string to the text returned of the result
if the search_string is not "" then exit repeat
end repeat

repeat
display dialog "Replace With:" default answer "" buttons {"Cancel", "OK"} default button 2
set the replacement_string to the text returned of the result
if the replacement_string contains ":" then
beep
display dialog "A file or folder name cannot contain a colon (:)." buttons {"Cancel", "OK"} >default button 2
else if the replacement_string contains "/" then
beep
display dialog "A file or folder name cannot contain a forward slash (/)." buttons {"Cancel", >"OK"} default button 2
else
exit repeat
end if
end repeat


set the item_list to list folder source_folder without invisibles
set source_folder to source_folder as string
repeat with i from 1 to number of items in the item_list
set this_item to item i of the item_list
set this_item to (source_folder & this_item) as alias
set this_info to info for this_item
set the current_name to the name of this_info
set change_flag to false
if the current_name contains the search_string then
if the folder of this_info is false then
set the change_flag to true
end if
if the change_flag is true then
-- replace target string using delimiters
set AppleScript's text item delimiters to the search_string
set the text itemlist to every text item of the current_name
set AppleScript's text item delimiters to the replacement_string
set the new itemname to the text itemlist as string
set AppleScript's text item delimiters to ""
my set item_name(thisitem, new itemname)
end if
end if
end repeat

beep 2

on set item_name(thisitem, new itemname)
tell application "Finder"
--activate
set the parent containerpath to (the container of this_item) as text
if not (exists item (the parent containerpath & new itemname)) then
try
set the name of this_item to new itemname
on error the error_message number the error_number
if the error_number is -59 then
set the error_message to "This name contains improper characters, such as >a colon (:)."
else --the suggested name is too long
set the error_message to error_message -- "The name is more than 31 >characters long."
end if
--beep
tell me to display dialog the error_message default answer new itemname >buttons {"Cancel", "Skip", "OK"} default button 3
copy the result as list to {new itemname, button_pressed}
if the button_pressed is "Skip" then return 0
my set item_name(thisitem, new itemname)
end try
else --the name already exists
--beep
tell me to display dialog "This name is already taken, please rename." default answer >new itemname buttons {"Cancel", "Skip", "OK"} default button 3
copy the result as list to {new itemname, button_pressed}
if the button_pressed is "Skip" then return 0
my set item_name(thisitem, new itemname)
end if
end tell
end set itemname