The se:webservice call has it's resulttype set to DataTable and the result could be loaded into a DataSet, but the DataSet doesn't contain any tables.

When the resulttype of the se:webservice macro has been set to DataTable, the response will first be loaded into a DataSet. Then, from the DataSet, the first DataTable will be returned. However, when this exception occurs, the DataSet doesn't contain any tables.

You could try to set the resulttype to string or use inline formatting xml to display the "raw" result. This way, you will be able to see the exact response and might be able to figure out why there are no DataTables within the loaded DataSet.