DECLINE BUSINESS INVITATION
It is an honor to be invited to [INVITATION, ex. attend a tour of your new premises]. Indeed, I would love to come. However, [REASON FOR REFUSAL, ex. I am attending a compressor technology conference in New York on the 14th.] I am sorry, therefore, that I cannot attend.
[STATE WHEN YOU NEXT EXPECT TO SEE THE RECIPIENT, ex. I look forward, nonetheless, to our lunch meeting on the 17th.]