I am writing to thank you for your kind invitation.
I was really pleased to receive it but I am sorry to miss the opportunity of celebrating your 25th wedding anniversary. I won’t be able to make it because I will go on a business trip on that day. It’s important to me as I have never had an occasion to go abroad. Moreover I can get a higher bonus.
It’s such a pity because we haven’t met outside working hours for ages.
Thank you again for the invitation and I hope we will have the opportunity to meet some other time.