Syntax error: missing semi-colon

Question

After a few days working and reading about tikz and with everyone help, I'm starting to reach my goals. One of my graphs was working ok, but I decided to make it accept "parameters", hence I would be able to animate it and update for many situations and here follows my snippet:

\documentclass[12pt]{article}
\usepackage{tikz}

\begin{document}
\begin{tikzpicture}[scale=2,y=-1cm]
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% INPUT PARAMS 

% Domain start (xy)
\pgfmathsetmacro\xn{1};
\pgfmathsetmacro\yn{1};

% Stencil order
\pgfmathsetmacro\o{2};

% Size of stencil
\pgfmathsetmacro\s{0.1};
% Size of domain
\pgfmathsetmacro\d{1};

% Stencil position
\pgfmathsetmacro\sx{7};
\pgfmathsetmacro\sz{3};


% Number of subdomains
\pgfmathsetmacro\nx{3};
\pgfmathsetmacro\nz{3};

% END OF INPUT PARAMS
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% Limits
\pgfmathsetmacro\Mx{max(\xn-2*\s,0)};
\pgfmathsetmacro\My{max(\yn-2*\s,0)};
\pgfmathsetmacro\mx{min(\xn+\d+(2*\s),\nx)};
\pgfmathsetmacro\my{min(\yn+\d+(2*\s),\nz)};

% Grid
\draw [step=\s cm,very thin,black!10] (0,0) grid (\nx,\nz);
\draw [step=\d cm,thick,black!40] (0,0) grid (\nx,\nz);
\draw [very thick,black] (0,0) rectangle (\nx,\nz);

%Stencil

% Horizontal
\fill [color=blue] (\Mx + 3*\s - \o*\s, \My + \sz*\s) rectangle (\Mx + 3*\s + \o*\s, \My + (\sz+1)*\s);

% Numbering
\foreach \ix [evaluate={\x=int(\ix-1);}] in {1,2,...,\nx} {
    \foreach \iz [evaluate={\z=int(\iz-1);}] in {1,2,...,\nz} {
        \pgfmathsetmacro\t{int(\x+\nx*(\z))};
        \node  [anchor=north west] at (\x,\z) {\t};
    }
}

\draw [->,purple] (\xn + .25*\d  , \yn + .25*\d) -- (\xn +0.75*\d,\yn+.75*\d);
\fill [color=yellow,fill opacity=0.1] (\Mx,\My) rectangle (\mx, \my);

\end{tikzpicture}
\end{document}

Its failing with:

! Package tikz Error: Giving up on this path. Did you forget a semicolon?.

See the tikz package documentation for explanation.
Type  H <return>  for immediate help.
 ...                                              

l.2480 ...ngle (\Mx + 3*\s + \o*\s, \My + (\sz+1)*
                                                  \s);

That is probably related with line:

\fill [color=blue] (\Mx + 3*\s - \o*\s, \My + \sz*\s) rectangle (\Mx + 3*\s + \o*\s, \My + (\sz+1)*\s);

But I can't see the reason why. Thanks.

EDIT (added answer)

For sake of reference I will add the fixed code here

\documentclass[12pt]{article}
\usepackage{tikz}

\begin{document}
\begin{tikzpicture}[scale=2,y=-1cm]
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% INPUT PARAMS 

% Domain start (xy)
\pgfmathsetmacro\xn{1};
\pgfmathsetmacro\yn{1};

% Stencil order
\pgfmathsetmacro\o{2};

% Size of stencil
\pgfmathsetmacro\s{0.1};
% Size of domain
\pgfmathsetmacro\d{1};

% Stencil position
\pgfmathsetmacro\sx{7};
\pgfmathsetmacro\sz{3};


% Number of subdomains
\pgfmathsetmacro\nx{3};
\pgfmathsetmacro\nz{3};

% END OF INPUT PARAMS
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% Limits
\pgfmathsetmacro\Mx{max(\xn-2*\s,0)};
\pgfmathsetmacro\My{max(\yn-2*\s,0)};
\pgfmathsetmacro\mx{min(\xn+\d+(2*\s),\nx)};
\pgfmathsetmacro\my{min(\yn+\d+(2*\s),\nz)};

% Grid
\draw [step=\s cm,very thin,black!10] (0,0) grid (\nx,\nz);
\draw [step=\d cm,thick,black!40] (0,0) grid (\nx,\nz);
\draw [very thick,black] (0,0) rectangle (\nx,\nz);

%Stencil
\fill [color=blue!70] (\Mx + \sx*\s - \o*\s, \My + \sz*\s) rectangle ({ \Mx + (\sx+1)*\s + \o*\s}, {\My + (\sz+1)*\s});
\fill [color=blue!70] (\Mx + \sx*\s, \My + \sz*\s - \o*\s) rectangle ({ \Mx + (\sx+1)*\s}, {\My + (\sz+1)*\s + \o*\s});
\fill [color=red!70] (\Mx + \sx*\s, \My + \sz*\s) rectangle ({ \Mx + (\sx+1)*\s}, {\My + (\sz+1)*\s});

% Numbering
\foreach \ix [evaluate={\x=int(\ix-1);}] in {1,2,...,\nx} {
    \foreach \iz [evaluate={\z=int(\iz-1);}] in {1,2,...,\nz} {
        \pgfmathsetmacro\t{int(\x+\nx*(\z))};
        \node  [anchor=north west] at (\x,\z) {\t};
    }
}

\draw [->,purple] (\xn + .25*\d  , \yn + .25*\d) -- (\xn +0.75*\d,\yn+.75*\d);
\fill [color=yellow,fill opacity=0.1] (\Mx,\My) rectangle (\mx, \my);

\end{tikzpicture}
\end{document}

Answer 1

Use

(\Mx + 3*\s + \o*\s, {\My + (\sz+1)*\s});

Instead of

(\Mx + 3*\s + \o*\s, \My + (\sz+1)*\s);

the ()'s inside the coordinate confuses the parser, adding a set of {} hides the inner ()'s from the coordinate parser.