File ended while scanning use of \next

Question

\documentclass[xcolor={dvipsnames}]{beamer}
\usetheme{Warsaw}
\usecolortheme[named=NavyBlue]{structure}

\usepackage[italian]{babel}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}
\usepackage{amsthm}
\usepackage{hyperref}
\usepackage{graphicx}
\usepackage{lmodern}
\graphicspath{{img/}}


\title{Analisi di un modello matematico per la malaria}
\begin{document}
    \titlepage  
\section{Introduzione}

   \begin{frame}[fragile]
    \textbf{La Malaria} è  una malattia infettiva,causata da un parassite e trasmessa agli umani attraverso la puntura di una zanzara.
      \begin{figure}
       \centering
             \includegraphics[height=0.60\textwidth]{mtt} 
\end{figure}
        $N_{h}=S_{h}+E_{h}+I_{h}+R_{h} $ \textit{Totale popolazione umana}
         \\ $N_{v}=S_{v}+E_{v}+I_{v} $ \ \   ~ ~ \textit{Totale zanzare}
    \end{frame}

   \section{Il Modello Matematico}

    \begin{frame}
     $ \frac{\mathrm{d}S_{h}}{\mathrm{d}t}=\Lambda_{h}+\psi_{h}N_{h}+\rho_{h}R_{h}-\lambda_{h}(t)S_{h}-f_{h}(N_{h})S_{h} $
     \\$ \frac{\mathrm{d}E_{h}{\mathrm{d}t}=\lambda_{h}(t)S_{h}-\nu_{h}E_{h}-f_{h}(N_{h})E_{h} $
     \end{frame}

 \end{document}

Answer 1

Troubles with \next cause option fragile because your \end{frame} has spaces before it. Here you have two options: (i) not use option fragile or (ii) move the \end{frame}.

Beside it you also have unbalanced parenthesis in fraction of the last equation. I also little bit reformatting your code:

\documentclass[xcolor={dvipsnames}]{beamer}
\usetheme{Warsaw}
\usecolortheme[named=NavyBlue]{structure}

\usepackage[italian]{babel}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}
\usepackage{amsthm}
\usepackage{hyperref}
\usepackage{graphicx}
\usepackage{lmodern}
%\graphicspath{{img/}}


\title{Analisi di un modello matematico per la malaria}
\begin{document}
    \titlepage
\section{Introduzione}


   \begin{frame}[fragile]
\textbf{La Malaria} è  una malattia infettiva,causata da un parassite e trasmessa agli umani attraverso la puntura di una zanzara.
    \begin{figure}
    \centering
\includegraphics[height=0.40\textwidth]{example-image}
    \end{figure}
    \begin{itemize}
\item[] $N_{h}=S_{h}+E_{h}+I_{h}+R_{h}$ \textit{Totale popolazione umana}
\item[] $N_{v}=S_{v}+E_{v}+I_{v}$       \qquad \textit{Totale zanzare}
    \end{itemize}
\end{frame}

   \section{Il Modello Matematico}

    \begin{frame}
    \begin{align*}
\dfrac{\mathrm{d}S_{h}}{\mathrm{d}t}
    & = \Lambda_{h}+\psi_{h}N_{h}+\rho_{h}R_{h}-\lambda_{h}(t)S_{h}-f_{h}(N_{h})S_{h}
      \\
\dfrac{\mathrm{d}E_{h}}{\mathrm{d}t}
    & =\lambda_{h}(t)S_{h}-\nu_{h}E_{h}-f_{h}(N_{h})E_{h} 
    \end{align*}
     \end{frame}

 \end{document}

Since I haven't your image, I use example-image provided by graphicx package and comet path to your image.