Note that you must be on current master (specifically, more recent than 0a6120cb) for LyX to detect this error.
To reproduce, go to File > New from Template > ACM-sigplan View with PDF (pdflatex). I get the following error: ! Undefined control sequence. \@toappear ...ent http://dx.doi.org/10.1145/\@doi <argument> ...n is removed.]\par \else \@toappear \fi \if \@reprint \noinden... Any ideas for a fix? Scott