Here’s a Blue’s post as well for your reference, from:
Howdy!
If the space is available it’s very likely some type of permission or other block is occurring causing the Blizzard app to not be able to allocate that space. Try checking the following:
- Check your permissions for the following folders: Repair the Application Support folder , and Repair the Shared Folder Permissions .
Next we do not support installing the game on Case-Sensitive Volumes or FileVault encrypted drives.
Thank you.