Applescript Help req. as script not working under 10.6.2

Apologies if this is posted in the wrong place. I'm hoping someone can assist me with the following script which was kindly written for me a while ago. It worked for ages but now produces an error message. Does it need tweaking or rewriting?

I use the script to automatically sort files into folders which are created from a selected number of letters from the filenames. AT the moment I'm getting the message...

"error "Finder got an error: Can’t make \"500 Gb HUB 1ownloads:JD: Thumbs Created - CHECK: FACES:Manuelas-2" into type item." number -1700 from "500 Gb HUB 1ownloads:JD: Thumbs Created - CHECK: FACES:Manuelas-2:" to item"

Any help is much appreciated. Thanks.


--script---

set baseFolder to choose folder
set {ATID, AppleScript's text item delimiters} to {"", "-"}
tell application "Finder"
set theFiles to every file of entire contents of baseFolder as alias list

set s_c to text returned of (display dialog "Please enter the STARTING character:" default answer "")
set e_c to text returned of (display dialog "Please enter the ENDING character:" default answer "")
repeat with aFile in theFiles
set fileName to name of aFile
set collection to text s_c through e_c of fileName
set cont to container of aFile as string

if folder (cont & collection) exists then
else
make new folder at cont with properties {name:collection}
end if
-- The next line trims the file name as so given a file name "GroupAbcSubGroupDefViewXYZFile012345-0"
-- and entering Start: 9 End: 19 then when the file is moved the new name would be "SubGroupDefViewXYZFile012345-0"
-- To retain the text prior to the character start (assuming there is any) remove the following line.
-- set name of aFile to (text s_c through -1 of fileName)
move file aFile to (cont & collection & ":")
end repeat
end tell
set AppleScript's text item delimiters to ATID