G'Day Rod,
I'm not a computer expert, but I use a freeware program called Irfanview.
Its a great little program.
The site rejected the photo because, in this case the photo was more than 600 pixels high (660).
If you load Irfan you just go to image / resize resample and set one of the pixel dimensions to either 800 wide or the 600 high. I hope that helps. I don't know of anything in the normal microsoft office suite that will do that. If anyone knows I'd be keen to learn.
Hope it helps for what its worth. I hope I don't sound like I know what I'm doing.