When you're in a drawing the sketch lines get placed on a view and if you happened to pick up the wrong view bounding box then it makes life difficult..
When you draw a line when your in a drawing pick a view - right click and select Lock View Focus
A little trial an error with the different views and the Lock View will be all you need....
One thing I have found that often if you select a dimension and it does not Highlight I thought I could do nothing with it. But I tried selecting on and when I did not highlight I just hit Del anyway and it went away. Not sure why it does that but somebody else on here mentioned that was what they do.
Also like was said above you have to be in that view. I have moved the view completely off the page to work on it so other bounding boxes do not cause me problems.