This is a brief letter or FAX explaining the need to reschedule an appointment. Putting it in writing keeps all the facts straight and if there is a future problem, it will serve as a reminder of what transpired. Explain why it is important to reschedule the meeting. Don't leave it open ended. Be specific about when you will contact the reader again.
1234, Main Street
Boston, MA 02123
08 April, 2005
<Recipient Address Goes Here>
Unfortunately I must reschedule our <meeting/appointment> on <original time and place>. <Reason(s) and explanation(s).>
By waiting <amount of time>, I feel our meeting will be much more valuable. I will call to reschedule a time to meet <time frame>. If you have any questions in the meantime, please don't hesitate to call me at <phone number>.
Thank you for your patience and understanding.
encl: <List of enclosed items goes here>