I cannot compile your code either on my system or on http://live.contextgarden.net/. I don't know what the error might be, but I'm not able to compile it.
Yeah, that one's all my fault. I copy-pasted my working code to the e-mail, then decided to add one little change (the extra \blackrule), and promptly introduced an error. Forgot to close the \smash{ braces.
_< Correct code below.
Cheers, Sietse \setupinterlinespace[line=3.2ex] \usemodule[simplefonts] \setmainfont[UnifrakturMaguntia] \starttext xAAgfas\smash{\blackrule[height=1ex]}\smash{\blackrule[height=2mm]} \\ xAAgfas\smash{\blackrule[height=2ex]} \\ xAAgfas\smash{\blackrule[height=3ex, color=red]} \\ xAAgfas\smash{\blackrule[height=3.2ex, color=blue]}\\ \stoptext