Problem in combining header, table, and href

Question

I am trying to make a specific header for the first page while the header for the rest of the pages will be the same but different from the first page. The header for the first and the second pages is shown below (only top portion of each page is shown), where the header is basically a table. My first question is how I can put a \href inside this table. I actually followed the instruction that was provided here but the compiler does not allow me to use \href. The other question is how I can create the second header different from the first page.

Here is the code I used.

\documentclass{article}
\usepackage[margin=1in,headheight=5\baselineskip,headsep=1\baselineskip,includehead]{geometry}
\usepackage{tabularx}
\usepackage{graphicx}
\usepackage{multirow}
\usepackage{hyperref}

\newlength{\headerwidth}
\setlength{\headerwidth}{\textwidth}
\newsavebox{\myheader}
\begin{lrbox}{\myheader}%
    \begin{minipage}[b]{\headerwidth}
    \renewcommand{\arraystretch}{1}%
    \begin{tabularx}{\headerwidth}{p{0.75\linewidth}p{0.25\linewidth}}
        {\bf FirstName LastName} & \\
        Address1 & Phone +1 (123) 456 7890 \\
        Address2 & Fax +1 (123) 456 7890\\
        Address3 & \href{mailto:myname@x.yz}{myname@x.yz}\\
    \end{tabularx}
    \end{minipage}
\end{lrbox}

\usepackage{fancyhdr}
\pagestyle{fancy}
\renewcommand{\headrulewidth}{0pt}
\renewcommand{\footrulewidth}{0pt}
\lhead{}
\chead{\usebox{\myheader}}
\rhead{}
\lfoot{}
\cfoot{}
\rfoot{}

\usepackage{lipsum}
\begin{document}
\lipsum[1-3]
\end{document}

Answer 1

\href should be used only after \begin{document}. Surround the lrbox with \AtBeginDocument{...}:

\AtBeginDocument{%
  \begin{lrbox}{\myheader}%
    \begin{minipage}[b]{\headerwidth}
    \renewcommand{\arraystretch}{1}%
    \begin{tabularx}{\textwidth}{@{}Xl@{}}
        \textbf{FirstName LastName} & \\
        Address1 & Phone +1 (123) 456 7890 \\
        Address2 & Fax +1 (123) 456 7890\\
        Address3 & \href{mailto:myname@x.yz}{myname@x.yz}
    \end{tabularx}%
    \end{minipage}%
  \end{lrbox}%
}

Note that I have changed the column Definition to @{}Xl@{} to avoid an overfull hbox. And I have removed the \\ behind \href.

Alternatively you can use \newcommand\myheader{...} instead of saving the table in a lrbox.

\documentclass{article}
\usepackage[margin=1in,headheight=5\baselineskip,headsep=1\baselineskip,includehead]{geometry}
\usepackage{tabularx}
\usepackage{fancyhdr}
\pagestyle{fancy}
\renewcommand{\headrulewidth}{0pt}
\renewcommand{\footrulewidth}{0pt}
\fancyhf{}
\chead{\myheader}
\newcommand\myheader{%
    \begin{minipage}[b]{\textwidth}
    \renewcommand{\arraystretch}{1}%
    \begin{tabularx}{\linewidth}{@{}Xl@{}}
        \textbf{FirstName LastName} & \\
        Address1 & Phone +1 (123) 456 7890 \\
        Address2 & Fax +1 (123) 456 7890\\
        Address3 & \href{mailto:myname@x.yz}{myname@x.yz}
    \end{tabularx}%
    \end{minipage}%
}

\usepackage{lipsum}

\usepackage{hyperref}% normally the last package

\begin{document}
\lipsum[1-3]
\end{document}

---

One possibility to get an other header on all pages except the first page is creating a new pagestyle firstpage and using \thispagestyle{firstpage}:

\documentclass{article}
\usepackage[margin=1in,headheight=5\baselineskip,headsep=1\baselineskip,includehead]{geometry}
\usepackage{tabularx}
\usepackage{fancyhdr}
\pagestyle{fancy}
\chead{other pages}
\renewcommand{\headrulewidth}{0pt}
\renewcommand{\footrulewidth}{0pt}
%
\fancypagestyle{firstpage}{% new pagestyle
  \fancyhf{}
  \chead{\myheader}}
  \newcommand\myheader{%
      \begin{minipage}[b]{\textwidth}
      \renewcommand{\arraystretch}{1}%
      \begin{tabularx}{\linewidth}{@{}Xl@{}}
          \textbf{FirstName LastName} & \\
          Address1 & Phone +1 (123) 456 7890 \\
          Address2 & Fax +1 (123) 456 7890\\
          Address3 & \href{mailto:myname@x.yz}{myname@x.yz}
      \end{tabularx}%
      \end{minipage}%
}
%
\usepackage{lipsum}

\usepackage{hyperref}% normally the last package
\begin{document}
\thispagestyle{firstpage}
\lipsum[1-10]
\end{document}