These errors occur when the first argument to plots[pointplot] or plots[pointplot] is not a set of points of numeric values specified in the proper format.  For the correct syntax, see the plots[pointplot] and plots[pointplot3d] help pages.

Example 1

The variable $x$ is undefined:

Solution:

Defining the variable fixes this error.

Example 2

Lowercase $\mathrm{pi}$$$is used instead of uppercase $\mathrm{Pi}\.$

Solution:

Using uppercase $\mathrm{Pi}$corrects the error.

You can also use the $\pi$ symbol from the Common Symbols palette.