This error occurs when you run out of space on your hard drive while downloading a game.
Free up hard drive space
There are several ways to free up hard drive space on your computer. Please check out this Microsoft article for instructions on ways to do this: Free up drive space in Windows
Change installation directory
If you have more than one hard drive try installing the game on a different one as it may have more free space. You can change this immediately after you click Install on a any game in your Library:
Free up hard drive space after install
You can also free up some hard drive space after you install Fortnite. This can be done by removing features, like High Resolution Textures, that are not needed.
- In the Epic Games Store click on Library in the left column.
- Find Fortnite.
- Click on the three dots next to the game.
- Select Options.
You will now see all the installed features.
- Uncheck the features you do not need.
- Click on the Apply button.