Error: You cannot upload this type of file
Please make sure the file is either gif or jpg. .jpeg files must first be renamed to .jpg files.

I keep getting an error message about the height or width of my picture, or no message at all.
Please ensure your picture is below 3000 pixels wide, 1000 pixels high and with a filesize of less than 2Mb.

On a Windows PC, you can edit the picture by doing the following:
Load Paint (Start, Programs, Accessories, Paint),
Load your picture,
Click Image, Stretch/Skew,
Stretch the image by 50% both horizontally and vertically,
Save and upload.

You can check if the picture is small enough to upload via Paint as well:
Click Image, Attributes,
Make sure Pixels is selected,
Check the values are less than 3000 x 1000,
Note: Do not change these values directly, it will cut part of your picture off.