Error inserting sales order via API

Error inserting sales order via API

I am trying to insert Sales Orders records but it gives me this error: [code] => 4832 [message] => Problem occurred while processing the request. This is my xml:
<SalesOrders>
    <row no="0">
        <FL val="Subject">118</FL>
        <FL val="Account Name">test test</FL>
        <FL val="Billing Street">test addr addr2</FL>
        <FL val="Billing City">Roma</FL>
        <FL val="Billing State">Roma</FL>
        <FL val="Billing Code">00100</FL>
        <FL val="Billing Country">IT</FL>
        <FL val="Shipping Street">test addr</FL>
        <FL val="Shipping City">Roma</FL>
        <FL val="Shipping State">Roma</FL>
        <FL val="Shipping Code">00100</FL>
        <FL val="Shipping Country">IT</FL>
        <FL val="Product Details">
            <product no="0">
                <FL val="Product Name">Test2 Deal</FL>
                <FL val="Quantity">2</FL>
                <FL val="Unit Price">50</FL>
                <FL val="List Price">50</FL>
                <FL val="Total">100</FL>
            </product>
        </FL>
    </row>
</SalesOrders>

The error occurs if i add the products. If I remove the <product no="0"> tag and its contents I don't get the error. So I can insert orders without products. When I insert an empty <product> tag I get the error again. And I don't understand why the error code is 4832 which means "Text value given for an Integer field".

Thanks.