Applescript not working in external USB Drive

Hi, first of all, thanks for reading this, I’ve been working in this project for hours long and I’m really confused right now.

I need to build an applescript to open a .pdf file located in the same directory as the app, I found this code, which worked great while testing from my hard drive.

--set the name of the file to open
property fileName : "file.pdf"
--get the path to the containing folder
set myPath to (path to me as string)
set AppleScript's text item delimiters to ":"
set the parentFolder to ¬
((text items 1 thru -2 of myPath) & "") as string
set AppleScript's text item delimiters to ""
-- find the flash file
    set targetFile to alias (the parentFolder & fileName)
on error
    --ie if there's no file here by this name, it will quit.
    return quit
end try
-- open the file
tell application "Finder"
    open file targetFile
end tell

The problem is, when I copy the application folder to a pendrive (that will be the final destination for my application) the script stops working. The .app will run but won’t open the .pdf. I’m really a newbie to Applescript, I can understand what that script does more or less but I don’t know what could be the problem as this is the first time I make an application for OSX.

Please, could you help me find where the problem is?

BTW, the pendrive is a FAT32 disk as it must run in Windows too. (same thing in windows is done via .bat files with “start” command)

Thank You

This works for me on the pen drive I have handy which is also formatted FAT32

property fileName : "TViX_M6500 English.pdf"
tell application "Finder"
		open file ((container of (path to me) as Unicode text) & fileName)
	end try
end tell