ok, Monsberg is the former german name in former Austrian-Hungarian Empire until 1919 of present Majšperk, now in Slovenia.it´s south of Graz, Styria, Austria about the border and also south of Maribor. it´s in former Untersteiermark/Lower-Styria which is now slovenian:
http://de.wikipedia.org/wiki/Maj%C5%A1perk
http://en.wikipedia.org/wiki/Maj%C5%A1perk
http://maps.google.at/maps?hl=de&cp=8&gs_id=7&xh...
former Untersteiermark: http://www.oelm.at/wp-content/uploads/Untersteiermark-JPG.jp...
old map with "Monsberg"- scroll to the corner right side above and then go down to 20 at right side. you find it little bit left of this number. Monsberg is written in shortform there > Monsbg:
http://lazarus.elte.hu/hun/digkonyv/topo/200e/33-46.jpg
http://en.wikipedia.org/wiki/Duchy_of_Styria

you can ask at the diocesan-archive in Maribor(former Marburg) if they have your ggrandfather in there files(birth): http://www.mariborska-metropolija.si/ustanove/arhiv.php

did the ancestors have german or slovenian lastnames? the question is if they had german or slavic orgin.