The guestbook has a php core, so it wiill not work in preview unless you install an Apache/php environment on your local computer.
Even so, i am not sure you will be able to preview, as BV generates the Preview code in the temp folder, whilst a local Apache / php environment have their own folder on your cimputer (if installed).

Further more BV is set to upload the necessary php core ONLY when it publishes (which happens only on VodaHost servers)

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