updateRecords - no permisiion

Hello,

I wrote an api to update records by ID. I crated a new custome field named ID and I insert int to it in the leads. My api is:

$xmlData = '<Leads>

<FL val="affStatus">'.$newstatus.'</FL>

</row>

</Leads>';

$id = '123456789';

$post=array("id"=>$id,"xmlData"=>$xmlData);

//--curl--//

I get:

You do not have the permission to edit this record or the "id" value you have given is invalid.

Why I don't have permission?

Thanks