[Plugin: Secure Invites] "SQL query could not be completed"

When using the template tag, I get this error returned to me by mail:

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A user just tried to invite someone to join Surfbird. The following SQL query could not be completed:

insert into wprc_invitations
(user_id, invited_email, datestamp)
values
(1, ‘[email protected]’, now());

The error reported was:

MySQL server has gone away

This is an automatic email sent by the Secure Invites plugin.
=========================================================

Any idea what could be wrong? Thank you!

http://ww.wp.xz.cn/extend/plugins/wordpress-mu-secure-invites/