Hi Mike,
The
InternalApiError.UNEXPECTED_INTERNAL_API_ERROR you are encountering indicates that it could be a temporary issue in the servers or could be due to a bug and is usually not associated to rate exceeded errors. You may refer
here for more information regarding rate limits and to this
guide for the exact values associated to operational limits.
As for the issue at hand, could you confirm if you are encountering this intermittently? Additionally, if the issue persists, kindly send to me the generated SOAP request and response so I can further investigate. You may reply via the Reply privately to author option.
Thanks and regards,
Peter
AdWords API Team