Microsoft announced the release of a 12.1.4 update to Mac Office 2008 that fixes an Entourage bug introduced with the last update:

Weve been working hard for the last week and a half to bring Entourage users todays 12.1.4 update. Its incredibly frustrating when we get through a release process and a new issue is introduced by an update. When we start to hear feedback and customer reports about issues with an update, I simply cringe because so much work goes into preventing that from happening. Unfortunately, the recent Office for Mac 2008 12.1.3 update introduced a bug that prevented some Entourage users from sending meeting invites to others. Were sorry.

The update is available for download.