[nomenclature] missing $ inserted.

[Maka Mohu]

Hi!
When I get an error with lyx.

! Missing $ inserted.
<inserted text>
                $
l.1478 ...ture[XX HH  $\left[\left[\right]\right]^

{n}$]{$\left[\left[\right]...


 I exported the file to pdflatex and found that this line is the source of
the problem (the part in \nomenclature[]). Any idea what is wrong?

{} \nomenclature[XX HH
$\left[\left[\right]\right]^{n}$]{$\left[\left[\right]\right]^{n}$}{A term
that is evaluted at time level n.}

Thanks.
/Maka