InfoPath and PSI UpdateCustomFields erroring

I'm pretty new to InfoPath and to the PSI webservices and I'm receiving the error "“The data contained a DataSet Diffgram whose associated schema in the WSDL is not supported," when I try to create a data connection in InfoPath 2010 and use the UpdateCustomFields method/operation. 

If I select other methods, such as ReadCustomFields, it seems to work just fine.

I'm using http://server/instance/_vti_bin/PSI/CustomFields.asmx?wsdl as the webservice in the Data Connection Wizard.  I get the list of methods/operations, but get the error when I select UpdateCustomFields and click next.  If I select ReadCustomFields, I am prompted to connect the parameters for that method to elements on my form.

I need the update to work to update the custom fields in Project Server 2010 (on SharePoint 2010) through InfoPath forms.

As I said, I'm fairly new to all of these applications, so if you need anything more, please let me know.

Thanks in advance!