帮忙写篇很简单的英语信

Dear ZhangMing:
Thanks for your invitation ang happy birthday to you. But to my unluckiness, I'm afraid I've no time to attend your birthday party.I would not be in ShangHai at that time since I have something important to do.I'd like to meet you and celebrate your birthday with you very much. Sorry again for my absence. I will pay a visit on you as soon as I come back to ShangHai.
yours
sincerely
XXX

Dear Ming,

Thanks for your invitation. I'd like to attend your birthday party, but due to some important issues, I'm afraid I was not in Shanghai on that day, thus cannot attend the party. I am awfully sorry about that.

I wish you a very happy birthday and have fun on the party. Hope I can join you next time.

Sincely your