FactoryTalk View XY plot disabled

Hi all,
Does anybody know why XY plot option could be disabled in the new trend properties for a new trend in FTView? I ran out of ideas...

I've broken the wall! Once I added pens and re-opened the properties dialog (just Applying is not enough), I got the option enabled! Thanks everyone who looked.

I know this has been a long time, but did you get the XY plot to work correctly? In FTV 9.0 my Y axis pen does not move on the x axis, only in the Y direction, even though the X axis pen value increases. What am I missing? It used to work...