I am not certain how prevalent this issue is in the wild and/or if anyone else has encountered it or had to workaround it, but there is a documentation bug that had me pulling my hair our for nearly a week.
If you have a need to get the members of an Exchange public distribution group using Exchange Web Services (EWS) ExpandDL operation via SOAP, and you followed this documentation, you will have encountered this super unhelpful error:
The problem is that the documentation is wrong. The namespaces used and the namespace prefixes are wrong. Here is what is on the documentation site:
What I ended up doing was to use the EwsEditor tool and Fiddler (per the guidance of an awesome Exchange guru I work with – thanks Dan!), and I captured the proper soap coming from the Managed API. To get ExpandDL to work properly, you need this SOAP:
Anyway, I will be issuing an update to easyEws very soon to include the correct SOAP.