What is an example of an excuse letter for not attending a meeting?

A missed meeting:

I'd like to express my regret for having missed the meeting of October 8, 2011. I had expected to attend as usual, but a family emergency occurred on the morning of the 8th and by the time I realized I wouldn't be able to make the meeting, it was past time for the meeting. I send my apologies to you and the committee for this oversight.

Sincerely,

Notice of inability to attend:

I'm writing to advise you that I will be unable to attend the meeting of October 8, 2011. Due to a scheduling problem, I will be out of town until the 9th of October. Upon my return, I will contact the secretary for a copy the minutes and any additional information so that I will up to date on the proceedings. I send my apologies to you and the committee.

Sincerely,

Turning down an invitation: Thank you for invitation to attend your meeting of October 8th 2011. I am advising you that I couldn't succeed in getting permission from my agency to participate in this meeting. I want you to know that I do appreciate your kind invitation.

Sincerely,

NOTE: These are sample reasons for not attending, use the real reason that you will not be able (were not able) to attend. A fabricated excuse can adversely affect your position in the long term.