You have already been told that you should perhaps read the provided error messages and then act on them such as installing the missing LaTeX packages, but one could actually help, if you provided a minimal example file, ie one where EVERYTHING has been taken out which does not contribute to the failure.
Most often the problem solves itself, because once the issue has been isolated the solution presents itself. In any case this is not a LyX issue, but a LaTeX one, etoolbox is present on MacTeX 2012, but then I have no idea about MikTeX. el on 2012-07-29 02:19 Josh Britt said the following: [...] > ! LaTeX Error: File `etoolbox.sty' not found. [...]
