[AS] Problem setting a var to geometric bounds

Hi,
I am trying to set a var to geometric bounds of identified object and get a error message.
Assuming that a page item is labeled "LogoBox"

tell application "Adobe InDesign CS3"
tell active document
set myobj to page items whose label is "LogoBox"
--if myobj exists then display dialog "Hey, I do exist !"
set objbounds to geometric bounds of myobj --(1)
end tell
end tell

(1) here is the error message I get :

i "Impossible dobtenir geometric bounds of {rectangle id 192 of page id 178 of spread id 173 of document \"file_1.indd\" of application \"Adobe InDesign CS3\"}."
>meaning that the script can't obtain geometric bounds...

Where is the error ? Thanks for help in advance.
Loic