Cannot graph invalid dim error
This error show up when you are graphing out of the plot menu. If you are not graphing data points from list menu, you need to turn the plots off. In the y= screen, you will see the words plot 1, plot 2, etc across the top of the screen. If one of the plots is highlighted (black box over the words), you need to turn it off. This can be done by arrowing up and highlighting the box and pressing enter. When you arrow back down, the plot should be off and you will be able to enter an equation in the y= lines and graph.
If you are graphing from the plot menu, this error lets you know that one of the lists you are graphing is longer than the other.
Another way to fix the problem is to reset the calculator by pressing 2nd button then plus sign then 7 then 1 then 2. This will reset the calculator however if you are graphing from lists, your data will be erased. Hope this helps.