invalid boundry region to join faces Please note that I'm new to Blender.

I was watching tutorials on YouTube. In the second tutorial I watched, there is part about modeling the default cube. It says to put the cube in Edit Mode then key X for the Deletion Pop Up Menu and select Dissolve Verticies. However, when I select dissolve vertices, I get the error message Invalid boundary region to join faces. That message is not shown in the tutorial. How can I fix this?
That is because the vertices you are located on more than one axes.
All the vertices have to be on a single axis.