Applescript - AppleEvent handler failed on set properties {visible messages: }

Question

I have the following applescript working under Lion, but it returns this Error: -10000. Mail got an error: AppleEvent handler failed. error under Yosemite.

try
tell application "Mail"
    set theViewer to front message viewer
    set theMsg to messages of theViewer
    set msgList to {}
    repeat with thisMsg in theMsg
        if read status of thisMsg is false and flagged status of thisMsg is false then
            set the end of msgList to thisMsg
        end if
    end repeat
    if msgList is {} then
        display dialog "There are no read messages in this mailbox."
    else
        tell theViewer to set properties to {visible messages:msgList}
    end if
end tell
on error the errMsg number the errNmb
if the errNmb is not -128 then
    set the errTxt to "Error: " & the errNmb & ". " & the errMsg
    display dialog the errTxt buttons {"Cancel"} default button 1
else
    error number -128
end if

end try

Any help would be appreciated.

Answer 1

From comments…

As it would appear that many people across the net are struggling & failing to get set properties to {visible messages:msgList} to work at all, it might be simpler in the long run to just pop up a count of unread/unflagged messages & optionally sort by flagged then unread for easy discovery in the Mail window.

I added in a 'sort by date or flags/unread' option in the dialog, too

tell application "Mail"
    tell the front message viewer
        set unReadMsgs to every message whose read status is false and flagged status is false
        display dialog ("There are " & (count of unReadMsgs) as string) & ¬
            " Unread/Unflagged messages." buttons {"Sort Unread", "Sort Date"} ¬
            default button "Sort Date" giving up after 300
        set theResult to button returned of result as string
        if theResult is "Sort Date" then
            set properties to {sort column:date received column}
        else if theResult is "Sort Unread" then
            set properties to {sort column:flags column}
            set properties to {sort column:message status column}
        end if
    end tell
end tell