When Steam is unable to download and store game data to your computer’s storage drive during the download, installation, or update of a previously installed game, the Steam disk write error message appears. Here are a few of the most common causes:
1. Drive or Steam folder permissions may be write-protected.
2. Physical defects exist in the hard drive.
3. Steam can be blocked by a firewall or antivirus software.
4. Outdated or corrupt Steam files.