AppleScript: System Events - delete

Question

I've been trying to get System Events delete command to accept multiple files and no matter how I try to preset the files to the delete command I get an error.
According to the dictionary entry for System Events - delete it would appear it should take multiple files:
delete v : Delete disk item(s).
delete disk item : The disk item(s) to be deleted.
This is what I have
tell application "System Events"
          set ss to every disk item in desktop folder whose name contains "Screen Shot" and name extension is "png"
  delete ss
end tell
And this is the log window
tell application "System Events"
  get every disk item of desktop folder whose name contains "Screen Shot" and name extension = "png"
  --> {file "Mac OS Lion:Users:frank:Desktop:Screen Shot 2013-03-22 at 14.31.02 .png", file "Mac OS Lion:Users:frank:Desktop:Screen Shot 2013-03-22 at 14.31.17 .png"}
  delete {file "Mac OS Lion:Users:frank:Desktop:Screen Shot 2013-03-22 at 14.31.02 .png", file "Mac OS Lion:Users:frank:Desktop:Screen Shot 2013-03-22 at 14.31.17 .png"}
  --> error number -1700 from {file "Mac OS Lion:Users:frank:Desktop:Screen Shot 2013-03-22 at 14.31.02 .png", file "Mac OS Lion:Users:frank:Desktop:Screen Shot 2013-03-22 at 14.31.17 .png"} to reference
Result:
error "System Events got an error: Can’t make {file \"Mac OS Lion:Users:frank:Desktop:Screen Shot 2013-03-22 at 14.31.02 .png\", file \"Mac OS Lion:Users:frank:Desktop:Screen Shot 2013-03-22 at 14.31.17 .png\"} into type reference." number -1700 from {file "Mac OS Lion:Users:frank:Desktop:Screen Shot 2013-03-22 at 14.31.02 .png", file "Mac OS Lion:Users:frank:Desktop:Screen Shot 2013-03-22 at 14.31.17 .png"} to reference
Now if I do
delete item 1 of ss
the file is deleted. Also if I do a repeat through the list I can delete each file.
I've tried every which way I can thing of to play with the list to get multiple files to delete with no success. But I have to admit that file references still send me to the book to get it right.
So what basic bit of AppleScript vodoo am I missing or is this one of those cases where the dictionary does not match the code?
thanks

Answer 1

The only way I've ever been able to get that to work is to do the delete immediately:
tell application "System Events"
          delete (disk items of desktop folder whose name contains "Screen Shot" and name extension = "png")
end tell
it seems that when you store it into a variable, system events no longer accepts it.  The only reason I can think for this is that the scripting dictionary asks for a disk item rather than a list of disk items.  It's possible that editing the scriptSuite files to tell it to accept a list would solve the issue, but I've never experimented.