documentclass[11pt]{scrbook}%

begin{document}
frontmatter

subject{The subject}
title{My Title here}
subtitle{Subtitle here}

vspace{5in}% replacing this by  vspace*{5in} did not help

author{Joe Doe}
date{today}
maketitle

mainmatter
chapter{My main Chapter is here}
test
end{document}

documentclass[11pt]{scrbook}%

begin{document}
frontmatter
begin{titlepage}
subject{The subject}
title{My Title here}
subtitle{Subtitle here}

vspace{5in}

author{Joe Doe}
date{today}
end{titlepage}
maketitle

mainmatter
chapter{My main Chapter is here}
test
end{document}