If you use VBA inside of 32bit AutoCAD you will have noticed that it is around 1000x times slower when running the same VBA code inside of 64bit AutoCAD.
This is because AutoCAD 64bit ships with the 32bit VBA DLL in a separate out-of-process executable rather than loading the VBA DLL inside of AutoCAD itself. Therefore, a lot of marshaling is incurred communicating between the out-of-process VBA executable and 64bit AutoCAD.
Other issues you may be seeing: Run-time error ‘429’: ActiveX component can’t create object
The best solution is to install 32bit AutoCAD on 64bit Windows, here are the affected versions along with their solution text…
Your 64bit AutoCAD 2008 was never designed to run in Windows 10, Windows 8 or Windows 8.1 64bit (these versions of Windows are newer than AutoCAD 2008). In order for your AutoCAD 2008 to run as it did in previous versions of Windows, you need to follow these easy steps…
NOTE: These steps do not bypass normal Autodesk licensing/authorization, you should expect to use your own serial numbers in the normal way.