[E2010] [EWS] [C#] [Windows]: How do I assign public folder Permission to a distribution Group

Hi,

I have a little C# Form Application which should be create a Public Folder and assign permission for a Distribution Group in Exchange 2010.

I have found following in the EWS Documentation:

 FolderPermission fp = new FolderPermission();

 fp.UserId.PrimarySmtpAddress = "test@abc.com";

If i try this with a User Email it works as well. But if I try to set a Email address from a Distribution Group it will throw this Error:

"Invailid UserID"

Does anybody know, how to set Folder Permissions to a Distribution Group?

Thanks,

Julian