Beginning with AutoCAD 2000, every custom class must provide a drawing and maintenance version number. The drawing version number value corresponds to the release of AutoCAD that was current when the class was created. The maintenance version number value can be set to whatever is appropriate for your class. For ObjectARX built-in classes, the maintenance value will be set to zero every time the drawing version changes. The version values are defined in the acdb.h header file. The ACRX_DXF_DEFINE_MEMBERS macro was modified in AutoCAD 2000 to take two new arguments, DWG_VERSION and MAINTENANCE_VERSION:
#define ACRX_DXF_DEFINE_MEMBERS(CLASS_NAME,PARENT_CLASS,\
DWG_VERSION,MAINTENANCE_VERSION,PROXY_FLAGS,DXF_NAME,APP)
These two arguments specify the version when the class was introduced. You must provide these arguments; there are no defaults. They become data members of the AcRxClass, but they are not persistent, that is, they are not stored in the class section of DWG and DXF files.