A SSRS2005 scatter chart was upgraded to SSRS2012. Upon execution, all points are shown over a common x-axis position, randomly far right or far left.
* In the Chart Data pop-up, the "Category Groups" in the OLD rdl was empty. This is OK as it can be omitted.
* It appears that SSRS2012 REQUIRES "something" in the Category Groups, and thankfully, perhaps because someone realized they needed it for "backward compatibility", there's a "Use Details" option.
* Choose this and the scatter chart works...
* When the conversion code detects an EMPTY Category Group, plug in the "Use Details" choice AUTOMATICALLY.