抱歉未能抽空出席活動

Dear Ms. Ying Ying Panda,
Re: Your Invitation
Thank you very much for your invitation to the Grand Opening of the Panda House in Ocean Park on 1st July 2007, for which I am most honoured.
I regret to inform you that due to a previously arranged engagement, I shall not be able to attend your function.
Once again I express my sincere gratitude for your invitation. Wishing you every success on the day,
I remain
Yours truly,
Le Le Panda

I am sorry about cannot to find some to attendance activities.

如果你不想用 attendance 可以用 attend / assist at / present at / show up / turn out.

Hope can help you la ^_^

Sorry,I couldn't seem able to join the event

I regret to inform you that I will be unable to attention the activity.

上面位朋友亂答一通，文法錯晒。

I am sorry I will not be available for the event.
I am sorry I couldn't seem able to join the event.