Can't get end...Help?

Question

What Have I Done Wrong?
I appreciate that I am not the best coder in the world. In fact I have only just started coding. I know my Script could be better and that there are some, shall we say, rough edges. I wrote this Script to automatically check for updates because  OS X is not doing so. OS X Yosemite(and Mavericks before it) would do so manually but not on it's own accord. This despite me having all setting turned on, deleting and rebuilding the necessary files and reinstalling from scratch OS X.
Anyhow here is my Script, perhaps someone could tell me why when i run it as an Application it runs then says Can't get end -1728
thank you
tell application "Finder"
  set myfile to "/Library/preferences/com.apple.SoftwareUpdate.plist"
  if not (exists POSIX file "/Library/Preferences/com.apple.SoftwareUpdate.plist") then
  display dialog "I am sorry but the file Library/Preferences/com.apple.SoftwareUpdate.plist does not exist"
  end if
end tell
set sourcepath to POSIX path of myfile
do shell script "cp -r " & sourcepath's quoted form & " ~/Desktop/"
do shell script "plutil -convert xml1 /Users/touchdown/Desktop/com.apple.SoftwareUpdate.plist"
set myfile to "Users/touchdown/Desktop/com.apple.SoftwareUpdate.plist"
set thetext to (read myfile)
delete POSIX file "/Users/touchdown/Desktop/com.apple.SoftwareUpdate.plist"
end
tell application "System Events"
  tell property list file myfile
  tell contents
  set automaticcheckenabledcopy to value of property list item "AutomaticCheckEnabled"
  if automaticcheckenabledcopy = true then
  do shell script "softwareupdate -l"
  end if
  set automaticdownloadcopy to value of property list item "AutomaticDownload"
  if automaticdownloadcopy = true then
  do shell script "softwareupdate -d"
  end if
  set configdatainstallcopy to value of property list item "ConfigDataInstall"
  if configdatainstallcopy = true then
  do shell script "softwareupdate -i --install -a"
  end if
  set criticalupdateinstallcopy to value of property list item "CriticalUpdateInstall"
  if criticalupdateinstallcopy = true then
  do shell script "softwareupdate -i --install -r"
  end if
  end tell
  end tell
end tell
tell
  end tell

Answer 1

No Offence but I have looked there already. I have done the following
1) checked the settings are turned on in System Preferences/App Store
2)Checked the file /Library/Preferences/com.apple.SoftwareUpdate.plist is there and also that it has the relevant settings turned on
3)I have deleted the above file then gone back into System preferences/App Store and turned the settings off then on to rebuild the above file.
4)I reinstalled OS X Yosemite
5)I reinstalled OS X Yosemite from scratch (clean install)
6)I created a brand new Apple id and used that to log in with in case it is somehow my id
7)I followed Apple's steps to bypass proxy Server settings as in some cases if your internet connection goes through a proxy/secure proxy server and the traffic is inspected then the connection to apple's update serves is no deemed secure and no effort made to check for updates. Once i followed Apple's steps to the letter it still does not work
8)Tried logging on to various other networks
9)Made sure all software/apps/OS X is unto date
10) When I reinstalled OS X Yosemite I did not restore from backups and just started fresh in case it was an app/software
So you can see I have done practically everything I can think off to solve the issue. This is why I think it is more endemic than simply something I have done. My Girlfriend also has the same issue as me so the chances of both of us doing the same thing wrong (with nothing we do working)is remote.
I am thinking that the problem must be Apple's end on their servers as I do not think it is a problem with the OS or lots more people would have the same issue and it would be more wide spread than this.