I'm sorry I'm unable to attend your party.
I'm sorry I'm not able to attend your party.
I'm sorry I can't attend your party.
I'm sorry that I'm not able to attend your party.
Mi bedaŭras, ke ne eblos al mi ĉeesti vian festeton.
残念ながらあなたのパーティーには出席できません。
Partine katılamadığım için üzgünüm.