This error occurred because the exponent is not attached to a base. To create this error, you must actively go back after creating the exponent and erase the base. Using standard keystroke or palette entry, the base is included before a superscript or subscript can be added.
To fix this error, ensure that any superscripts or subscripts are attached to a base.
In this example, a subscript is missing the required base.
To fix the error, ensure the subscript is attached to a base.
This is the same type of error, but the missing base for the superscript is found inside the expression. The 2-D math parser returns a slightly different error, because it is interpreting the superscript as a base, which is invalid.
Just like the "empty script base" error, you must ensure that any superscripts or subscripts include a valid base.