Does your AutoCAD 2013 MASSPROP command produce an error or invalid results on some solids, then there's a hot fix for that.
Autodesk MASSPROP Hotfix
This hot fix addresses an issue with the MASSPROP command returning an error or invalid results on certain solids created by extruding regions along closed polylines.
This hotfix applies to the Service Pack 1 or 1.1 levels of AutoCAD 2013 and AutoCAD 2013-based vertical products.
To get the hotfix go to:
The readme is: