CivilCAD 2008 was released before AutoCAD 2010. The official 64-bit compatibility patch came via a hotfix from the developer (Domussoft/Diehl). Without that hotfix, the installer will block you, stating: "CivilCAD requires AutoCAD 2007-2009."
Despite the technical friction, this combination was highly sought after. AutoCAD 2010 introduced significant UI improvements (the Ribbon interface) and speed enhancements. Engineers wanted the stability of the 64-bit platform but needed the legacy project compatibility of CivilCAD 2008. civilcad 2008 para autocad 2010 64 bits