error number -1728 Applescript & some issues with spot

I have been working on this script for weeks. Basically I would like to batch (using AS) illustrator CS4 files. (open, find spot colors, change to process, save, close). So far I'm able to open files but the part when is supposed to change them into process is falling giving me an error number -1728 from document 1 of document 1. I tried to put as many --comments on the script
I want to clarify my knowlege in AS is basic. What is this error? I search specifically for this error number with no success. What I have was pieced together and modified from 2 scripts I found. I'm challenging myself with not too much success but If I don't to ask, I don't learn. Can you anyone guide me to a solution?

Code:

property file_types : {"EPSf", "EPSP"}
property file_extensions : {"eps"}
--Would like just Illustrator eps files not Photoshop eps. How can you do this? currently if in the folder there are Photoshop eps files the script is opening those files


set the_folder to (choose folder with prompt "Select the files containing Illustrator docs to change spot to process colors:")
set the_images to get_folder_list(the_folder, file_types, file_extensions, true, false)

 
if the_images = {} then
  beep
     display dialog "No valid Illustrator found in chosen folder." buttons {"OK"} default button 1 with icon 0 giving up after 10
     return
end if
 
on openLegacyFile(fileToOpen) --Open a file with automatic update of legacy text --(I found this in the ADOBE ILLUSTRATOR CS4SCRIPTING REFERENCE)
     tell application "Adobe Illustrator"
  activate
  open POSIX file fileToOpen as alias with options {update legacy text:true}
     end tell
end openLegacyFile


tell application "Adobe Illustrator"
  activate
  --set user interaction level of script preferences to never interact --Will ignore any dialogs when opening files. Currently NOT working with files with embedded color profiles I'm getting a message: Your current settings discard CMYK profiles in linked content but profiles were set to be honored when this document was created. Cancel/Continue
  
     repeat with the_image in the_images
  open the_image as alias
         tell document 1
 
               set locked of every layer to false --unlock all layers
               set locked of every page item to false --unlock any page items
               set selected of (every page item) to true
               set spotColorCount to count of spots
 
               try
                   set color type of (spots of document 1 whose name is not "[Registration]" and its color type is spot color) to process color
               end try
               if exists (swatches whose class of color of it is CMYK color info) then
                   set t to (name of every swatch whose class of color of it is CMYK color info)
                   my convertSpotSwatchesToProcess(t)
               end if
  --This is the part that is not working at all. It doesnt find any spot colors
-- the results is --> error number -1728 from document 1 of document 1

 
 
  --set user interaction level of script preferences to interact with all --restore prefs
         end tell
     end repeat
end tell


on convertSpotSwatchesToProcess(list_of_swatches)
     tell application "Adobe Illustrator"
         tell document 1
               set replacementSwatches to {}
               set deleteSwatches to {}
               set cmykSwatches to every swatch whose class of color of it is CMYK color info and name is in list_of_swatches
               repeat with thisSwatch in cmykSwatches
                   set swatchName to name of thisSwatch
                   set swatchColor to color of thisSwatch
                   copy {name:swatchName, color:swatchColor} to end of replacementSwatches
                   set end of deleteSwatches to thisSwatch
               end repeat
  delete deleteSwatches
               repeat with thisReplacement in replacementSwatches
  make new spot at end with properties thisReplacement
               end repeat
         end tell
     end tell
end convertSpotSwatchesToProcess



on get_folder_list(the_folder, file_types, file_extensions)
     set the_files to {}
     tell application "Finder" to set folder_list to every item of folder the_folder
     repeat with new_file in folder_list
         try
               set temp_file_type to file type of new_file
               set temp_file_extension to name extension of new_file
         on error
               set temp_file_type to "folder"
               set temp_file_extension to ""
         end try
         if file_types contains temp_file_type or file_extensions contains temp_file_extension then set end of the_files to (new_file as string)
     end repeat
     return the_files
end get_folder_list

-I'm getting this results get file type of document file "Black.eps" of folder "test" of folder "Desktop" of folder "user" of folder "Users" of startup disk --> missing value