Ok, the long winded story of "what happened":
I bought a board. It worked.
Either computer.
Alas it was an Ether TEN board and the shield didn't fit over the RJ45 connector, so I bought another "UNO" equivalent.
It too worked. Either computer.
The UNO is used in my alarm clock - the main reason I got into Arduino. It works.
Nowadays it is only programmed from my laptop.
It still can be.
The Ether TEN board was being used in my potted plant watering system and I accidently fried it. Power on non-power pins.
It sort of works, but does silly things now and then. Too unreliable.
I bought another "UNO compatible".
This one won't flash sketches on either computer.
I took it to a mate's place who is into Arduino and it won't flash there - same error. To me: Pointing to the board.
Suspecting the board, I went back to the shop - with laptop - and tried another board.
The boards at the shop have different connectors on them, so a new cable had to be used - supplied with the board.
SAME PROBLEM.
So: So far I know:
The laptop can flash my alarm clock. (No, I can't start swapping chips. I need the alarm clock.) But the cable works, the laptop works, and the board work.
New board: It has this NOT IN SYNC error.
Went to shop, new board, new cable.
NOT IN SYNC.
Tried another board - this time an Ether TEN.
NOT IN SYNC.
Hmmmm......
Went to another shop and bought a genuine UNO.
This has yet another connector type.
Got home.
NOT IN SYNC.
Tried on other computer.
NOT IN SYNC.
This is:
NEW BOARD, NEW CABLE, DIFFERENT COMPUTER.
I get my old Ether TEN board - which had my old plant watering sketch.
Flashed the BLINK sketch.
LED 13 blinks.
Flash it with my sketch. LED 13 stops blinking.
Flash it with BLINK and it starts blinking again.
PROVEN: The machine can talk to the boards ok.
When I try to flash BLINK to the new board, the RX/TX LEDs do blink a bit, but not as much as with the Ether TEN board, and I get a NOT IN SYNC error.
Try the BLINK sketch on the Genuine UNO board: SAME.
Tried changing the BOARD TYPE in the IDE. SAME.
Have checked Device manager and I am selecting the correct COM port. The board is listed and is known.
Other things to mention:
I have both 1.0.1 and 1.0.2 installed.
NEITHER ONE can upload to the two new boards.
Indulge me:
What speed do the com ports have to be set at?
I did notice I can select the board type/name and the com port, but not the settings like speed, parity, stop bit, etc.
Though I guess if I can flash the BLINK to my faulty Ether TEN, the settings should be ok.