Use of \scshape or \textsc in beamer \institute

The small caps command has not the desired effect if your font doesn't provide a small caps shape. If necessary, switch to a font family which supports it. Here's an example showing that it works with \rmfamily:

\documentclass{beamer}
\title{A sample document}
\subtitle{for demonstrating small caps in an institute name}
\author{Author}
\institute{Dipartimento di Tecnologie dell'Infomazione \\
  Corso di Laurea  in: {\rmfamily\scshape Sicurezza dei Sistemi e delle
  Reti Informatiche}}
\date{\today}
\begin{document}
\maketitle
\end{document}

So the solution is, choose another font or at least another font weight, family or shape of which there's a small caps variant.