ESP8266 Wifi error: 'String' does not name a type

I am trying to build a project for an ESP8266 board (D1 Mini Lite) and am having a problem with the WiFI library. The sketch I a using to test is below and does nothing really but include the ESP8266WiFi.h file.

I get a series of errors starting with the following. It looks like that Arduino String object is not getting included properly. I have included platformio.ini contents as well. Am I missing something simple here?

In file included from /Users/andrebaskin/.platformio/packages/framework-arduinoespressif8266/libraries/ESP8266WiFi/src/ESP8266WiFi.h:31:0,
from /Users/andrebaskin/.platformio/packages/framework-arduinoespressif8266/libraries/ESP8266WiFi/src/ESP8266WiFi.cpp:25:
/Users/andrebaskin/.platformio/packages/framework-arduinoespressif8266/cores/esp8266/IPAddress.h:86:31: error: ‘String’ does not name a type

// sketch
#include <Arduino.h>
#include <ESP8266WiFi.h>

void setup() {
// put your setup code here, to run once:

void loop() {
// put your main code here, to run repeatedly:

// platformio.ini
platform = espressif8266
board = d1_mini_lite
framework = arduino

Not reproducable for me.

Dependency Graph
|-- <ESP8266WiFi> 1.0 (C:\Users\Maxi\.platformio\packages\framework-arduinoespressif8266\libraries\ESP8266WiFi)
"esptool" -eo "C:\Users\Maxi\.platformio\packages\framework-arduinoespressif8266\bootloaders\eboot\eboot.elf" -bo .pioenvs\d1_mini_ard\firmware.bin -bm dio -bf 40 -bz 4M -bs .text -bp 4096 -ec -eo .pioenvs\d1_mini_ard\firmware.elf -bs .irom0.text -bs .text -bs .data -bs .rodata -bc -ec
MethodWrapper(["checkprogsize"], [".pioenvs\d1_mini_ard\firmware.elf"])
Memory Usage ->
DATA:    [===       ]  32.6% (used 26676 bytes from 81920 bytes)
PROGRAM: [==        ]  24.7% (used 258016 bytes from 1044464 bytes)
 [SUCCESS] Took 7.45 seconds 

Make sure you update your PlatformIO and all the platforms.

You set me on the correct path. What I ended up doing was to uninstall both Atom and Platformio including deleting all the associated files. Then I did a new clean install of Atom and Platformio. Now the compile is clean and I can start to migrate sketches over from the Arduino IDE. Thank you very much.