Generic Web Service and xmlgregoriancalendar date format

Hi, I'm trying to connect to a WSDL and pass values to it using the Generic Web Service node. I can connect to the WSDL fine, but when I try to pass a date of birth date using the node I get an error saying the date is in the wrong format and cannot be parsed. The date format is meant to be passed as xmlgregoriancalendar date format. Does anyone know the correct format syntax that can be shared please? I've tried so many different options of date formats and always get the Java parsing error. I thought the correct format was 1980-04-18T00:00:00, but I have tried many many alternatives.
Has anyone successfully used the Generic Web Service node by parsing the xmlgregoriancalendar format, and if so could you provide an example of the date notation that is parsable?
Thanks for your help, and I love Knime by the way!