WP-QuickLaTex not working at all

Hi, I installed WP-Quicklatex, activated it and enabled it.
I create a simple post copying the LaTex example in the plugin configuration page:

[latexpage]
At first, we sample $f(x)$ in the $N$ ($N$ is odd) equidistant points around $x^*$:
\[
f_k = f(x_k),\: x_k = x^*+kh,\: k=-\frac{N-1}{2},\dots,\frac{N-1}{2}
\]
where $h$ is some step.
Then we interpolate points $\{(x_k,f_k)\}$ by polynomial
\begin{equation} \label{eq:poly}
P_{N-1}(x)=\sum_{j=0}^{N-1}{a_jx^j}
\end{equation}
Its coefficients $\{a_j\}$ are found as a solution of system of linear equations:
\begin{equation} \label{eq:sys}
\left\{ P_{N-1}(x_k) = f_k\right\},\quad k=-\frac{N-1}{2},\dots,\frac{N-1}{2}
\end{equation}
Here are references to existing equations: (\ref{eq:poly}), (\ref{eq:sys}).
Here is reference to non-existing equation (\ref{eq:unknown}).

I added it without using the visual editor.
The result us completely messed up. The majorities of tags don’t work and are visible (such as \begin{}, \frac{}, \sum etc). Only \left seems to wokr, and the equations are numbered (with the number overlapping the equation content.)

I’m using the theme Independent Publisher 2