Please upgrade your firmware.
That's the shipping firmware from 2013. Lots of fixes since then.
http://www.support.xerox.com/support/workcentre-7800-series/file-download/enus.html?operatingSystem=macosx&fileLanguage=en&&associatedProduct=WorkCentre-78xx-built-in%20controller&contentId=123551&from=downloads&viewArchived=false
That's the shipping firmware from 2013. Lots of fixes since then.
http://www.support.xerox.com/support/workcentre-7800-series/file-download/enus.html?operatingSystem=macosx&fileLanguage=en&&associatedProduct=WorkCentre-78xx-built-in%20controller&contentId=123551&from=downloads&viewArchived=false