LyX: Problems with title when writing in Memoir document style

LyX: Problems with title when writing in Memoir document style

I am pretty new both to LyX and to TeX.SX, and have no LaTeX background. I'm writing my master's thesis in LyX and have just changed the document style from book to book (Memoir). When I try to export to pdf (using pflatex), I get two error messages (1 and 2 below):
1)
Argument of \reserved@a has an extra }.
2)
Paragraph ended before \reserved@ was complete.
The explanations read:
1)
{\Large{ Masteroppgave i lingvistikk}}}
I've run across a `}' that doesn't seem to match anything.
For example, `\def\a#1{...}' and
`\a}' would produce this error. If you simply proceed now, the `\par'
that I've just inserted will cause me to report a runaway argument
that might be the root of the problem. But if your `}' was spurious,
just type `2' and it will go away.
2)
{\Large{ Masteroppgave i lingvistikk}}}
I suspect you've forgotten a `}', causing me to apply this
control sequence to too much text. How can we recover?
My plan is to forget the whole thing and hope for the best.`
Masteroppgave i lingvistikk is the last part of the my title, simply meaning 'Master thesis in linguistics'. I have separated my thesis title into three lines, using justified line breaks. All lines of the title are in title style, but they have different font sizes.
It seemed to work all right when I used the book document class, but after changing to Memoir something goes wrong.