Dear :
Please accept my apologies for the delay in acknowledging your invitation for on . I have been away form the office and only just returned.
Unfortunately, I have other plans for the date you mention, but shall be happy to make a date for some other convenient time.
Cordially,
亲爱的:
未能对您发来的出席举行的的邀请予以及时答复深表歉意。我因一直外出，刚刚返回。
很遗憾，由于有其他事务安排，故不能赴约。我很愿意在以后方便的时候前去拜会。