letmathcalundefined
DeclareMathAlphabet{mathcal}{OMS}{cmsy}{m}{n}

documentclass [invmat]{svjour}
usepackage[garamond]{mathdesign}
letmathcalundefined
DeclareMathAlphabet{mathcal}{OMS}{cmsy}{m}{n}
begin{document}
$mathcal{R}$
section{New Section}
$mathcal{S}$
end{document}

Use of reserved@a doesn't match its definition. [$mathcal{S}]
Undefined control sequence. [$mathcal{S}]

LaTeX Error: Too many math alphabets used in version normal. [$mathcal{S}]