While version 1.0001 was the very first update released shortly after the game's launch in 2007, it is rarely used today. Most players aim for (for specific old mods) or 1.0006 (the final official stable version). 1. Why version 1.0001?

Moving from 1.0000 to 1.0001 usually preserves saves, but moving backwards from a higher version will definitely break them.

Back then, patches were region-locked. You need the specific WorldWide , US , or CIS/Digital version of the patch to match your game disk/install.