Problem with last 12 months example

[Noreaster]

I'm trying to copy the example of "Chart the Last 12 Months Dynamically"
so I can understand it and use if for my purposes. The problem I'm having
with the example is where you see the Month and Year on the chart, I
have the values from value b column instead. I dont see what I may have
gone wrong.

I'm learning this on my own and its a bit overwhelming but you people have
been very helpful.

 

[Noreaster]

I found where the problem was, series, category, the data wasn't right. I don't
know why it had changed. The data I'm using runs left to right, so I'll be
figuring that out.