Entourage calendar sync

I've just been set up with a Mac at work (woo hoo!), but unfortunately the switch to Entourage is giving me grief.

I'm attempting to manage my boss' diary through entourage, but new meeting requests won't let me accept or decline. However, when I go into her calendar and double click on tentative meetings, I can!

It may seem like I've solved my own problem, but trust me, it gets stranger. Only some of the meetings I double click on allow me to alter her response. And to make matters worse, if she doesn't respond to meeting requests that come through, which she often doesn't, they don't appear in her calendar.

There's no common thread between the meetings I can alter - well, not that I can see anyway.

Does anyone have an answer to this problem?