Delete any corrupted library folders: %USERPROFILE%\Documents\V-Ray Material Library AND %PROGRAMDATA%\Chaos Group\V-Ray Material Library .
Starting with V-Ray 6, Chaos moved the preset library entirely into the Cosmos Browser. For V-Ray 5.2 users, the local library remains the primary method for offline access.
The library downloader may not work correctly with network paths starting with \\ . It is best to download to a local drive first.
If you are writing this text for a user guide or article, it is highly recommended to add the following warning:
Use the V-Ray Asset Browser . If files are missing, you can run the mtllib.exe tool (typically found in the V-Ray installation directory) to download the library assets.