Vertical line alignment with X-axis

Hello, all. As I am new here, I'd appreciate knowing if I overlooked some search that would have answered my question. I looked about and found nothing directly applicable, but sometimes that's just a matter of learning the right search terms.

So, I have a spreadsheet (2007) that has a graph. The primary x-axis consists of ordered UNIX timestamps. The primary y-axis is various metrics collected from a server. I'm trying to create a vertical line at certain timepoints so that it's easy to see the effect of certain actions on the server. I've gone through the Peltier example for a series-based vertical line, but I keep running into 2 strange problems:

1) The vertical line's placement seems completely unrelated to the timestamp that is part of the data series. See on the "Graph" sheet of the workbook -- I've placed dots on the data series where the line should appear. The vertical line is based on the little "Val" section to the left of the graph. It seems to insist on being way off to the right. The trick, it would seem, would be to get Excel to either use exactly the same values for the secondary horizontal axis as for the primary, or simply to use the primary horizontal axis for both vertical axes; but how? Or is there something I'm overlooking?

2) Whenever I try not to display the secondary axes, Excel crashes. What in the world could cause that?