Microtype package interaction with TikZ in baposter ("Giving up on this path..." error)

Question

I'm making a poster using baposter.cls (one can get it here). I wanted to use microtype package to increase the spacing of the letters in my headerbox titles but I've encountered a TikZ error : Package tikz Error: Giving up on this path. Did you forget a semicolon?. }.

I'm using Atom with latexmk for compilation, but I've also tried TeXStudio and the error persists. I'm running a fully up to date version of MikTeX.

Minimal working example

I left all the font packages in since they might be contributing to the error.

\documentclass[portrait,final,a0paper,fontscale=0.277]{baposter}

%% Fonts
\usepackage{bookman}
\usepackage[eulergreek]{sansmath}\sansmath
\usepackage{upgreek}
\usepackage[T1]{fontenc}

\usepackage{anyfontsize}
\usepackage[normalem]{ulem}
\usepackage{lipsum}

% https://tex.stackexchange.com/questions/62346/enlarging-tracking-letter-spacing
\usepackage[letterspace=50]{microtype}

\begin{document}
\begin{poster}%
{% poster options
    grid=false,%
    columns=3,%
    colspacing=1.5em,%
    bgColorOne=white,%
    borderColor=black,%
    headerColorOne=black,%
    headerFontColor=white,%
    boxColorOne=white,%
    textborder=rectangle,%roundedsmall,%
    headerborder=none,%
    headerheight=0.1\textheight,%
    headershape=rectangle,%smallrounded,%
    headershade=plain,%
    headerfont=\fontsize{11}{1}\selectfont\sf\lsstyle,%
    headerheight=0.13\textheight,%
    textfont={\setlength{\parindent}{1.5em}}\fontsize{7.5}{10}\selectfont\sf,%
    boxshade=plain,%
    background=plain,%
    linewidth=1pt%
}{}{Title}{author}{}{}

    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%    %%
    \headerbox{foo}%
    {name=ceas, column=0, row=0, span=3}%
    {
        \vspace{0.5em}
        \lipsum[1-4]
    }

    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
    \headerbox{bar}%
    {name=foo, column=0, span=3, below=ceas}%
    {
        \vspace{0.5em}
        \lipsum[5-8]
    }

\end{poster}
\end{document}

The above code reproduces the error. If one comments out the \lsstyle (which is the microtype command) the error goes away.

Answer 1

There are several weakness in the code. Happily, this particular one is easy to fix.

\documentclass[portrait,final,a0paper,fontscale=0.277]{baposter}

%% Fonts
\usepackage{bookman}
\usepackage[eulergreek]{sansmath}\sansmath
\usepackage{upgreek}
\usepackage[T1]{fontenc}

\usepackage{anyfontsize}
\usepackage[normalem]{ulem}
\usepackage{lipsum}
\usepackage{etoolbox}

% https://tex.stackexchange.com/questions/62346/enlarging-tracking-letter-spacing
\usepackage[letterspace=500]{microtype}

\makeatletter
\patchcmd\poster
 {\baposter@box@headerfont{\baposter@box@title}}
 {{\baposter@box@headerfont\baposter@box@title}}
 {}{}
\makeatother




\begin{document}
\begin{poster}%
{% poster options
    grid=false,%
    columns=3,%
    colspacing=1.5em,%
    bgColorOne=red,%
    borderColor=black,%
    headerColorOne=blue,%
    headerFontColor=white,%
    boxColorOne=white,%
    textborder=rectangle,%roundedsmall,%
    headerborder=none,%
    headerheight=0.1\textheight,%
    headershape=rectangle,%smallrounded,%
    headershade=plain,%
    headerfont=\fontsize{11}{13}\sffamily\lsstyle,%
    headerheight=0.13\textheight,%
    textfont={\setlength{\parindent}{1.5em}}\fontsize{7.5}{10}\sffamily,%
    boxshade=plain,%
    background=plain,%
    linewidth=1pt%
}{}{Title}{author}{}{}

    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%    %%
    \headerbox{foo}%
    {name=ceas, column=0, row=0, span=3}%
    {
        \vspace{0.5em}
        \lipsum[1-4]
    }

    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
    \headerbox{bar}%
    {name=foo, column=0, span=3, below=ceas}%
    {
        \vspace{0.5em}
        \lipsum[5-8]
    }

\end{poster}
\end{document}

I used 500 in order to emphasize that the letter spacing is done.

Please, note that \sf has been deprecated for more than 20 years.