Packet bigger than max_allowed_packet

Hi

I have just installed this plugin and am trying to clone the root of a multisite installation into a subsite. The subsite gets created, but I get an error

Uh-oh - there was an sql error: Got a packet bigger than 'max_allowed_packet' bytes.

I am assuming that I need to set max_allowed_packet in my server.cnf, but do I also need to set it in my client.cnf and my mysql-clients.cnf file too and if so then

• which sections do I set it in e.g. [ mysql] [mysqldump] etc ??
• what value do I use (and how to determine the best value)

Many thanks
Chris