Always start with the first file. Right-click ER_2GB.part01.rar and select "Extract Here" .
You cannot "open" part 4 individually. You must initiate the extraction from Part 1 . ER_2GB.part04.rar
The software will automatically read Part 04 and all other segments to reconstruct the game files. Always start with the first file
Many file-hosting services have a 2GB file size limit for free users. ER_2GB.part04.rar