Hello Ed.
You got that because you tried to create the folder in Application Support folder from the local domain (/Library/Application Support/).
Is there a reason for not creating the folder in the Application Support folder from the user domain (/Users/userName/Library/Application Support/)?
I ran :
set p2Library to path to library folder from user domain as text
set p2ApplicationSupport to p2Library & "Application Support:"
tell application "System Events"
make new folder at end of folder p2ApplicationSupport with properties {name:"dropBox setting"}
end tell
and wasn't asked to authenticate.
I tried with :
set p2Library to path to library folder from user domain as text
set p2ApplicationSupport to p2Library & "Application Support:"
tell application "Finder"
make new folder at folder p2ApplicationSupport with properties {name:"dropBox setting"}
end tell
and it worked too without asking to authenticate.