tcolorbox environment inside longtable — it is possible?

You must reset the before key. In the default it contains a \pagebreak and as longtable redefines \pagebreak you get errors. This here compiles:

\documentclass{article}
\usepackage{tcolorbox}
\usepackage{longtable}
\usepackage{lipsum}

\begin{document}

\begin{longtable}{|p{\linewidth}|}
\hline
\begin{tcolorbox}[before={}]
\lipsum[3]
\end{tcolorbox}
\\
\hline
\end{longtable}
\end{document}