I wrote some example for exam questions. I add my code below:
\documentclass[answers]{exam}

\pagestyle{headandfoot}
\runningheadrule
\firstpageheader{}{}{}
\runningheader{Variant A} {} {}
\runningfootrule
\firstpagefooter{}{}{}
\runningfooter{} {Page \thepage \enspace of \enspace \numpages} {}

\begin{document}

\begin{center}
\fbox{\fbox{\parbox{5.5in}{\centering
Answer the questions in the spaces provided on the
question sheets. If you run out of room for an answer,
continue on the back of the page.}}}

\end{center}

\vspace{0.1in}

\makebox[\textwidth]{Name and section:\enspace\hrulefill}

\vspace{0.2in}

\makebox[\textwidth]{Instructor's name:\enspace\hrulefill}

\begin{questions}

\question
 One of these things is not like the others' one of these things is not the same. Which one is different?
 \begin{oneparchoices}
        \correctchoice John
        \choice Paul
        \choice George
        \choice Ringo
        \choice Socrates
\end{oneparchoices}

\end{questions}

\end{document}

and I get an error like this:
ERR: 0/0 good answers not coherent for a simple question [0:]

How can I solve it?