Beginning after the 14.3.2 update to Mac Outlook 2011 released March 12, 2013, sending emails to both previously established and new contact groups in Mac Outlook 2011 results in the message being placed in the Drafts folder so that it is not sent and the error shown below in Figure 1 appears as a pop-up. The error message is "EmailAddress or ItemId must be included in the request."
Figure 1. Error message which appears in version 14.3.2 of Mac Outlook 2011 after sending a message to an unexpanded contact group.
To avoid this problem, when using a contact group, after typing in the group name, click on the two downward-pointing arrows to the left of the name, shown circled in Figure 2 below, to expand the contact group into a list of separate email addresses as show in Figure 3 below. Send the message.
Figure 2. Click on the two downward-pointing arrows inside the name of the contact group in the 'To:' line of the email address to expand the contact group into individual email addresses
Figure 3. Contact group after expansion into individual email addresses. This contact group contained four entries.
Long-term solution: We would expect Microsoft to release a fix for this problem in an upcoming update. This thread suggests that the fix might arrive in version 14.3.4 in May 2013.
For a Microsoft Exchange email system, it is possible to recreate the contact group in Outlook Web App, OWA, the browser version of email. Look under 'Contacts', New, 'Contact Group'. The advantage of a contact group created in OWA is that unlike a contact group created in Mac Outlook 2011, the group is available from any computer.