Destination folder seems invalid

Question

everything works except the line to move the file, the_dest seems to be invalid
tell application "Finder"
set the_selection to get selection as string
-- "ActiveProjectsA-D-1: TELETHON:ASIA187 Prasith's First Job Thailand:Nuendo Project:Audio:ASIA187 Prasith'S First Job Thailand FULL Mix v2.wav"
set the_selection2 to get selection
-- document file "ASIA187 Prasith'S First Job Thailand FULL Mix v2.wav"
if word 1 of the_selection contains "active" then -- we are on Apace
set AppleScript's text item delimiters to {":"}
set Nuendo_project to text item -3 of the_selection
set the_project to text item -4 of the_selection -- "ASIA187 Prasith's First Job Thailand"
set theexportfolder to text items 1 thru -3 of the_selection & "EXPORTS" as string
set word_one to text item 1 of the_selection
set the_dest to text items 1 thru 3 of the_selection & "EXPORTS" as string
set AppleScript's text item delimiters to {""}
end if
if Nuendo_project contains "Nuendo Project" then
--tell application "Finder" to duplicate (the_selection2) to folder (the_dest)
end if
end tell

Answer 1

What is the specific error message (if any) you get?
As written it won't work because of the line:
if Nuendo_project contains "Nuendo Project" then
but Nuendo_project is not defined anywhere in the script, therefore this test will fail and it will never get to the line that's supposed to copy the file. Maybe you mean:
if the_selection contains "Nuendo Project" then
If that's the case I'd change your logic a little - you're doing a lot of work manipulating the path without knowing whether you need to or not - it would be prudent to perform this check first and then do all the string manipulation and file copy within the if/end if block.