RequirePackage[absolute,overlay]{textpos}
setlength{TPHorizModule}{1cm}
setlength{TPVertModule}{1cm}
newenvironment{aside}{%
  letoldsectionsection
  renewcommand{section}[1]{
    parvspace{baselineskip}{Largeheadingfontcolor{dgreen} ##1}
  }
  begin{textblock}{3.6}(2.0, 0.55)
  begin{flushright}
  obeycr
}{%
  restorecr
  end{flushright}
  end{textblock}
  letsectionoldsection
}

begin{aside}
section{RegionA}
~
end{aside}

begin{aside}
section{RegionA}
begin{enumerate}
item foo
end{enumerate}
end{aside}

! LaTeX Error: There's no line here to end.

See the LaTeX manual or LaTeX Companion for explanation.
Type  H <return>  for immediate help.
 ...

l.75 begin{enumerate}