Тут в разделе caution написано:

CautionWhen running Svcutil.exe to get metadata for a service that exposes two different service contracts that each contain an operation of the same name, Svcutil.exe displays an error saying, “Cannot obtain Metadata from ....” For example, if you have a service that exposes a service contract called ICarService that has an operation Get(Car c) and the same service exposes a service contract called IBookService that has an operation Get(Book b). To work around this issue, do one of the following:

Rename one of the operations

Set the Name to a different name.

Set one of the operations' namespaces to a different namespace using the Namespace property.
Это вызвано ограничениями WSDL или это проблемы SvcUtil.exe, и можно найти другой кодогенератор, не имеющий такого ограничения?