Currently I'm using Magento 1.9.01 and PHP 5.3.28. In ASP .NET I'm trying to retrieve the catalog tree by using the SOAP API using the following code:
var magentoService = new MagentoService.Mage_Api_Model_Server_Wsi_HandlerPortTypeClient();
var sessionId = magentoService.login(userName, apiKey);
var categoryTree = magentoService.catalogCategoryTree(sessionId, "", "");
The errror I get is "Internal Error. Please see log for details." And in the logs I can see the following:
Argument 1 passed to Mage_Catalog_Model_Category_Api::_nodeToArray() must be an instance of Varien_Data_Tree_Node, null given
From what I've read it can be a bug with PHP 5.4 or greater, but not the version I'm using... So if someone has any idea how to solve this, it will be greatly appreaciated.
Seems pretty straight forward, though the error thrown suggests a much bigger problem. First make sure that the variables are exactly as you specified in your Magento installation (pay attention to caps). Second you can't pass empty strings, instead try "Null".
Good luck