I am trying to trace this object/image (it's a red cross which I have attached) to end up with just a outline of the red cross. Every time I perform a 'trace bitmap' it leaves the ends open, why???

I don't know for sure. My best guess would be because there's no white space between the cross and the edge of the image.

You could easily connect the ends yourself.

-- select the 2 end nodes with the Node tool
-- press "Join selected end nodes with a new segment" button on the contol bar, looks like this

For this, I would suggest using the Pen/Bezier tool, rather than Trace Bitmap. Trace Bitmap might add small distortions here and there.

Pen/Bezier tool is easy for this, especially if you use Snapping and a grid....or guides (http://tavmjong.free.fr/INKSCAPE/MANUAL ... pping.html)

-- click once on the canvas, where you want to start making the cross
-- press Ctrl, to keep the movement of the mouse perfectly horizontal or vertical (or 15 degree angles)
-- move the mouse to the next corner (keep holding Ctrl)
-- click once, move to the next corner
-- repeat until finished

Snapping and grid or guides will keep everything nice and square and symmetric.

I agree with Brynn, for this particular case I would even use Rectangle tool to create two long rectangles (or one and then double it and rotate) then Union them into a single cross object, and snap to grid to make it easier.