Double lines instead of single

Using Mac OS X draw a single line but two appear in parallel delete one and they both disappear.
Reloaded Make it a numher of time but to no avail.
Opened new page but problem persists.

This seems very strange and an issue I haven’t heard of before. Could you please provide more information about exactly what you did (what Tool you selected, what actions you took, etc.)? If you can upload a screenshot or better yet a model with the problem, that would help. Also, are you a newbie or do you have some SketchUp experience?

Also what Style active?