Define an Applescript in a field...

I'm having some difficulty writing my applescript in a field. I keep having an error of

"This text does not end in a quotation mark (") or is longer than 253 characters."

Can anyone help me understand to properly write the applescript in a field, particularly the proper logic of when to open and close quotation marks.

Below is my applescript: (it renames a file that was originally exported using export/xsl)

newsletter_refnum is the field that contains the unique reference number in the database.

set postname to """ & newsletter_refnum & """

tell application ""Finder""

try

set NLfilename to ""NL"" & postname as string

set folderPath to ((path to me) as string) & "Contents:Resources:""

set thefile to folderPath & ""NewsLetter.html""

if file thefile exist then

set name of file thefile to NLfilename & "".html""

move file thefile to desktop

else

display dialog ""NewsLetter.html was not succesfully created" buttons {"OK"}"

end if

end try

end tell"