The on-call hosting team have checked this out, and told me that there doesn't appear to be a general problem with SQL connections between the shared hosting server your site is on and the provided SQL server.
Is your SQL database hosted externally? (in which case you should check that server)
If hosted on an SQL database provided by Zen and the problem persists then you'll need to speak to support about it in the morning. It may be worth placing a holding page (which doesnt require an SQL connection) up in the mean time.
Sorry I couldn't be more help.
Kindest regards,
James Sweet
http://www.zen.co.uk