Type arguments cannot be inferred from usage

public OperationResult<string> ReadString(string address) {
    OperationResult<EfortData> read = this.ReadEfortData();
    if (!read.IsSuccess)
        return read.CreateFailedResult();
    ...
}

public OperationResult<A1> CreateFailedResult<A1>() => new OperationResult<A1>(this.ErrorCode, this.Message);