many thanks for your kind invitation and I shall be delighted to attend.
Thank you very much for your kind invitation. Unfortunately I won’t be able to make it. Best wishes for a great night and successful event which I am sure it will be.
Unfortunately I will be traveling at that time so will not be able to join.
Any further information needed, please do not hesitated to contact us.
Due to my change of plan, now I will not be able to attend the party.