Can't add a task to all tickets.

I have a Workflow to generate Zoho Desk Tickets via Zoho Creator.
Now i must add several Tasks to the generated Tickets.

everytime i will add a tasks to a Ticket, i become the Error:
<?xml version="1.0" encoding="UTF-8" ?>
<response uri="/api/xml/tasks/addrecords">
      <error>
            <code>4832</code>
            <message>Problem occured while processing the request</message>
      </error>
</response>

My Code:
testmap=Map();

        url=" https://desk.zoho.com/api/json/tasks/addrecords";
        XMLTaskRequest="<tasks><row no=\"1\">";
        XMLTaskRequest=XMLTaskRequest + "<fl val=\"CASEID\">" + ticket.SupportID.tolong() + "</fl>";
        XMLTaskRequest=XMLTaskRequest + "<fl val=\"Subject\">" + task.subject_field + "</fl>";
        XMLTaskRequest=XMLTaskRequest + "<fl val=\"Task Owner\">" + task.Owner + "</fl>";
        XMLTaskRequest=XMLTaskRequest + "</row></tasks>";

        testmap.put("authtoken", "123123123123123123");
        testmap.put("portal", "xxx");
        testmap.put("department", "yyy");
        testmap.put("xml", XMLTaskRequest);
        TaskResponse = postUrl(url,testmap);
        info XMLTaskRequest;

If i pick randomy a nother Ticket and Add a Tasks to it and it worked:
<?xml version="1.0" encoding="UTF-8" ?>
<response uri="/api/xml/tasks/addrecords">
      <result>
            <responsecode>2001</responsecode>
            <responsedata>
                  <Tasks>
                        <fl val="Status">Record(s) added successfully</fl>
                        <fl val="Time">2017-08-10 11:52:38</fl>
                        <record no="1">
                              <id>123412323</id>
                              <info><![CDATA[abcdefgh]]></info>
                        </record>
                  </Tasks>
            </responsedata>
      </result>
</response>

Only older tickets (and all working tickets where generated in Desk itselv not over the Creator or API).
I compare all fields of both Tickets to find out where the Problem is. I Also look via Reports in the Tables to get all Data to compare better but get no result or reason.

So can anyone tell me why i can add a task to one Ticket but not to another, by the API!?

TANK YOU!!!