Ground symbol issue in Circuitikz

This is absolutely normal: the symbol ground is a node shape, hence it mandatory to adopt the TikZ \node syntax.

Specifically, one should change

\draw (0,0) to [ground] (0,-1); 

into

\draw (0,0) to (0,-1) node[ground]{}; 

or the equivalent

\draw (0,0) -- (0,-1) node[ground]{}; 

A complete example:

\documentclass[tikz,border=10pt]{standalone}
\usepackage{circuitikz}
\begin{document}
\begin{circuitikz} 
\draw (0,0) -- (0,-1) node[ground]{}; 
\end{circuitikz}
\end{document}

The result: