Hi Nasser,
\documentclass[12pt]{article}
\usepackage{amsmath}
\begin{document}
$\widehat{\dbinom{\odot_\text{v}\odot}{\wr}}$
\end{document}
May be the latex code here is also not valid?. I did not write the above
latex code myself. I found it long time ago on the net. Do not remember now
from where.
Yes, this is the same case, you have \odot_\text{v} here. Subscripts need to be encloded properly in braces as well.
Best regards, Michal
