It looks like it might be some interaction between Parse::RecDescent and ActivePerl. A quick google search for "parse::recdescent errorprefix" yielded a number of ppm build error logs and a couple of references to use utf8. It looks like the utf8 issue was fixed in an earlier release (of Parse::RecDescent), and it also doesn't look like the code is explicitly working with utf8.

jethro showed that there's an issue with the grammar itself, so maybe PoorLuzer could try fixing up his grammar definition so that it passes, or whittling it down to the minimal case that causes the $errorprefix error.