Did you follow the links in my first response, RenderMan? In a nutshell: The command MakeObjectLayerCurrent was originally defined via lisp in the MNL file (c:ai_molc). Sometime around Acad2008 this was moved into Base Autocad. When the VLIDE is open an error is thrown about the protected symbol "ai_molc" being overwritten because the MNL STILL has the definition in it and it is attempting to redefine the one now embedded in Autocad proper. Removing, or renaming, the offending defun in the MNL file fixes this so it won't happen again (until the next upgrade, reinstall, whatever).