Problems calling the UPDATE Task API

Problems calling the UPDATE Task API

When calling the UPDATE API i always get a 400 error response with the content 6500 General error.

My HTTP Headers :

POST /restapi/portal/6437#####/projects/1042724000000######/tasks/1042724000000######/ HTTP/1.1

Form params content :

authtoken ##########6f2b60ae2#############
name Création du service Yoamo

person_responsible 6434#####
duration 0
duration_type hrs
custom_status 1042724000000148319

I am using similar technic for the CREATE call and it works fine.  I only do the update because you told me that "custom_status" cannot be set on creation.   What am i doing wrong ?

Thanks for your help.