Craft Edge

HI! I am trying to 'add 'a line into an inkscape 'photo'. I had inserted another line with no problem, did the convert to path then path union and it worked. I then tried adding 1 more line with the bezier tool, then as soon as I select both and click union the line I made disappears. Any idea what's happening?

Milangal,
Not familiar with this problem but will throw out some ideas.
Try viewing in the outline view (View>Display Mode>Outline) to see if the line is really disappearing. Sometimes it is set to no fill or color so it can't be seen although this doesn't sound like that since it is visible until you union them.
The status bar at the bottom of the text screen can sometimes give valuable info. Take note of what it says before during and after you click union.
Is the line you are trying to union a line or is it a closed path? I don't think you can use union without 2 closed paths.

Here is the file I am trying to edit. I am simply trying to add a 'bottom' to the wrist so it is a closed figure. You'll see that it let me close the lightening bolt but it won't let me do so on the wrist. AH! It let me, although it looks a bit funny, I changed to outline mode and it let me do it???????