Hi,
To better look into your issue, could you provide more information such as the AdWords API version you are using, your clientCustomerId and any SOAP request and response generated when you encountered the error? You may reply using Reply privately to author.
Additionally, this might also be a network issue on your end since the the behavior is inconsistent for both environments that you used. This said, you may also want to get in touch with the C#/.NET client library owners via this
link for additional assistance.
Best regards,
Peter
AdWords API Team