IPhone : IOS: getting '400 Bad Request' when using multipart/form-data

I am new IOS developer and I am facing a headache issue regarding to use multipart for uploading file and some text, i have tried a lot on here

The status code always return 400. I tired to test my web service with another way, such as build Rest client by HttpComponent API, using RestEASY client and both of them worked successfully, how funny!

Any suggestions will help my investigation

Thanks

An An