Trouble with repeat

Question

I have 2 folders open and 2 files on the desktop.
folder 1 named 12-17-13 Open Exports
folder 2 named 12-17-13 NDP Exports
file 1 named 12-17-13 Open mix.wav
file 2  named 12-17-13 NDP mix.wav
I just want to cycle through the 2 open windows, if a file on the desktop has the name 12-17-13 OPEN, then put that file in the folder with the similiar name.
when I go to copy the file,  I get "cant make file into an integer"? Any ideas  Camelot, you out there.
tell application "Finder"
          set base_path to "Macintosh HD:Users:Shawn:Desktop:"
          set the_promo_folders to the name of every Finder window whose name contains "exports"
          repeat with a_folder in the_promo_folders
                    set dest_folder to "Incoming_Projects:" & a_folder
                    set file_name to characters 1 thru -8 of a_folder as string -- 12-16-13 ndp
                    set the_mixes to (every file of the desktop whose name contains file_name)
                    repeat with a_mix in the_mixes -- 12-16-13 ndp mix.jpg
                              if name of a_mix contains file_name then
                                        set source_file to a_mix
  display dialog source_file as string
  display dialog dest_folder as string
  --try
  move file source_file to folder dest_folder
  --end try
                              end if
                    end repeat
          end repeat
  --delete the_mixes
end tell

Answer 1

I got it to work by swapping the mixes and the folders
tell application "Finder"
          set promo_folders to every folder in folder "Incoming_Projects:Open PM"
          set the_mixes to (every file of the desktop whose name contains "mix")
          repeat with a_mix in the_mixes
                    set source_file to a_mix
                    set file1 to name of a_mix
                    set the_name to characters 1 thru -8 of file1 as string -- 12-17-13 open
                    repeat with a_folder in promo_folders
                              set destination_folder to a_folder
                              if name of a_folder contains the_name then
                                        try
  move source_file to destination_folder
                                        end try
                              end if
                    end repeat
          end repeat 
end tell