Hi Gary, did you code upload successfully to the ESP32 board? Did you see “Done uploading”?
That error can be one of these things

1. It’s having trouble completing the code upload and it results in a crash and continuous reboot.
2. Or the ESP32 requires more power than your USB port can output (also resulting in continuous reboot)

Hi Rui, The code uploaded giving a “Done uploading” message. 
I thought I’d try the ESP-IDF running under mingw32 the msys2 shell launcher as suggested in the Espressif web site just to check the board was working properly. This works perfectly using the same USB port. I can build and flash the example c programs to the board without difficulty. I was wondering if the bootloader (if it needs one) requires reflashing in order to use the Arduino system. If so how is this done?
Thanks Gary

There’s no bootloader needed to run the ESP32 with Arduino code. Simply flashing an Arduino sketch should overwrite everything inside the ESP32 and run the Arduino code normally… 
What happens if you upload the sketch example and power the ESP32 with an external power supply?
Does the LED blink? I would just link to double-check if it’s a problem with power or not… 
NOTE: double-check that you are connecting the LED to the right GPIO in your code

Hi Rui,
I connected a 2 Amp 5v supply to the board and uploaded the Arduino blink sketch.
Same problem I’m afraid. Still outputs:
ets Jun 8 2016 00:22:57
rst:0x10 (RTCWDT_RTC_RESET),boot:0x13 (SPI_FAST_FLASH_BOOT)
configsip: 188777542, SPIWP:0xee
clk_drv:0x00,q_drv:0x00,d_drv:0x00,cs0_drv:0x00,hd_drv:0x00,wp_drv:0x00
mode:QIO, clock div:1
load:0x3fff0018,len:4
load:0xffffffff,len:-1
to the serial monitor.
The information panel under the sketch returns the following
esptool.py v2.1
Connecting….
Chip is unknown ESP32 (revision 1)
Uploading stub…
Running stub…
Stub running…
Changing baud rate to 921600
Changed.
Configuring flash size…
Auto-detected Flash size: 4MB
Compressed 8192 bytes to 47…
Writing at 0x0000e000… (100 %)
Wrote 8192 bytes (47 compressed) at 0x0000e000 in 0.0 seconds (effective 4369.1 kbit/s)…
Hash of data verified.
Flash params set to 0x002f
Compressed 14128 bytes to 9196…
Writing at 0x00001000… (100 %)
Wrote 14128 bytes (9196 compressed) at 0x00001000 in 0.1 seconds (effective 790.4 kbit/s)…
Hash of data verified.
Compressed 160192 bytes to 82030…
Writing at 0x00010000… (16 %)
Writing at 0x00014000… (33 %)
Writing at 0x00018000… (50 %)
Writing at 0x0001c000… (66 %)
Writing at 0x00020000… (83 %)
Writing at 0x00024000… (100 %)
Wrote 160192 bytes (82030 compressed) at 0x00010000 in 1.4 seconds (effective 887.5 kbit/s)…
Hash of data verified.
Compressed 3072 bytes to 122…
Writing at 0x00008000… (100 %)
Wrote 3072 bytes (122 compressed) at 0x00008000 in 0.0 seconds (effective 1890.5 kbit/s)…
Hash of data verified.
Leaving…
Hard resetting…
Any suggestions?
Gary

Hi Gary, I’ve never encountered that error before, so to be honest I don’t know how to fix that problem…
That sounds like a hardware problem: https://github.com/espressif/arduino-esp32/issues/801, (a pin that is connected to GND or something). (It can even be the ESP32 chip itself badly soldered to the dev board)
Which pin are you using to control the LED?