Check your total disk space metrics listed directly on the top screen. If the available blocks are lower than what your computer reports, hidden files are active.

Some technical references also suggest it could point to an "SDMC/NAND bus error," which relates to the system having trouble communicating with the storage media. This dual nature—pointing to either a space issue or a hardware communication issue—is why simply freeing up storage often isn't enough.

Delete unused games, applications, or existing CIA installers from the SD card to ensure you have at least double the size of the file you are trying to install. Use "Install and Delete": In the FBI menu, select the "Install and delete CIA"