documentclass{standalone}
usepackage{mathabx}
usepackage{ngerman}
begin{document}
$rightarrow$
end{document}

[...]MiKTeX2.9texgenericmathabxmathabx.dcl
! Missing number, treated as zero.
<to be read again>
                   protect
l.435 ...eMathSymbol{<}            {3}{matha}{"A0}

usepackage{ngerman}
usepackage{mathabx}