You probably have a wrong entry for that author, as the following example shows; upon compiling test.tex, which calls nonsense.ltb as recommended in the documentation of amsrefs, I get the following:

File test.tex
\documentclass{article}
\usepackage[author-year]{amsrefs}
\begin{document}
\ocite{Sokal96} recommends Bourbaki's
text~\cite{Bourbaki70} for a gentle introduction to set theory.
\begin{bibdiv}
\begin{biblist}
\bibselect{nonsense}
\end{biblist}
\end{bibdiv}
\end{document}
File nonsense.ltb
\documentclass{article}
\usepackage{amsrefs}
\begin{document}
\begin{bibdiv}
\begin{biblist}
\bib{Bourbaki70}{book}{
title={Th\'eorie des ensembles},
author={Bourbaki, Nicolas},
date={1970},
publisher={Hermann},
address={Paris}
}
\bib{Sokal96}{article}{
title={Trangressing the boundaries},
subtitle={Toward a transformative hermeneutics of quantum gravity},
author={Sokal, Alan},
journal={Social Text},
volume={46/47},
date={1996},
pages={217--252}
}
\bib{SokalB1998}{book}{
title={Fashionable Nonsense},
subtitle={Postmodern Intellectuals' Abuse of Science},
author={Sokal, Alan},
author={Bricmont, Jean},
publisher={Picador USA},
address={New York},
date={1998}
}
\end{biblist}
\end{bibdiv}
\end{document}
What can be wrong?
I get "Sokal Alan (1996)" in the first citation if the author field is
author={Sokal Alan},
without the comma.