Dear sir/madam:
  Thank you for your letter of [date]. I’m glad that you are also going to [place] next month. It would be a great pleasure to meet you at the [exhibition/trade fair].
  Our pany is having a reception at [hotel] on the evening of [date] and I would be very pleased if you could attend.
  I look forward to hearing from you soon.
  Yours sincerely,
  [name]