multiple recipient does not work

HI, ive installed contact form 7 to my wordpress website but when i tried to give the drop down option for users to select which email the message to send to, the form doesnt get sent and receives this error message: FAILED TO SEND YOUR MESSAGE….

ive read this thread, but i dont understand how to resolve my issue: http://wordpress.org/support/topic/getting-errorfailed-to-send-your-message-please-try-later-or-contact-the-admin?replies=12

following are my codes

<p>Office to Contact*

[select* office “Sydney | email.com.au” “Melbourne | email2.com.au”]</p>

<p>Your Name*
[text* your-name] </p>

<p>Your Email*
[email* your-email] </p>

<p>Subject*
[select* subject multiple “General” “Ticketing” “Sponsorship” “Others”]</p>

<p>Your Message*
[textarea* your-message] </p>

<p>[submit “Submit”]</p>

then in the mail, ive set the To: [office]

ive tested the form with setting the To: field to my own email and that worked.

Please help!

http://wordpress.org/extend/plugins/contact-form-7/