Your guestbook seems to be working fine here, though.
I suppose the message did not say defer defer, but perhaps defer="defer" as explained on this page?
Apr 2, 2012 - 1:37AM
Re: guestbook code not working
When I put the code for the guestbook on my site on google sites, I can't see it and there is this sentence:
ATTENZIONE: il codice HTML contiene alcuni tag che non sono consentiti. Questi sono stati rimossi dalle modifiche.
Warning: The HTML code has not-allowed tags. They have been removed.