isdone.dll (and other repacks like ) is a common unpacking error that occurs when the installer fails to decompress game data. It is rarely caused by a "missing" file and is instead typically linked to memory issues (RAM/Virtual Memory), antivirus interference, or corrupted download files. Level1Techs Forums Most Effective Fixes Increase Virtual Memory (Page File)

The error often hides a simple problem: not enough space.

A surprising number of isdone.dll errors stem from pathing issues.