Can't Decompress

[Bill Marriott]

I created a new stack with a single field and two buttons:

Button 1
--------
on mouseUp
  put "D:\Desktop\Put It Here" into saveFolder
  put "My Data File.xyz" into saveFileName
  put "binfile:" & saveFolder & "\" & saveFileName into saveURL
  answer saveURL
  put fld 1 into URL saveURL
 put compress(URL saveURL) into URL saveURL
end mouseUp

Button 2
--------
on mouseUp
  put "D:\Desktop\Put It Here" into loadFolder
  put "My Data File.xyz" into loadFileName
  put "binfile:" & saveFolder & "\" & loadFileName into loadURL

  put decompress(URL loadURL) into URL loadURL
  put URL loadURL into fld 1
end mouseUp

I've put the stack up on RevOnline for you to try. User MerryOtter.

Clicking Button 1 saves a file that is compressed properly. (I can even 
extract it with 7zip). Clicking Button 2 gives me the error:

Type: decompress: string is not compressed data
Object: Button 2
Line: put decompress(URL loadURL) into URL loadURL

What am I doing wrong? No matter what I do I can't get decompress to work. 
Rev 2.6.1 on Windows XP. (I hope I'm not missing something basic like I did 
with my last post...)