A corrupted ISO or WBFS file can also trigger this error.
Error Context:
This error occurs in Dolphin emulator (typically when modding or rebuilding disc images for GameCube or Wii games) during an attempt to modify the game’s filesystem. The FST (Filesystem Table) is a critical index inside a game ISO that lists every file’s name, offset, size, and attributes. When Dolphin’s internal iOSFS (a virtual IOS filesystem layer used for Wii titles) tries to save a modified FST back to the disc image, the write operation fails.
Typical Error Message:
iosfs failed to write new fst dolphin iosfs failed to write new fst
Dolphin may not have permission to modify the NAND files.
Fix:
Step 1 – Verify File & Folder Permissions A corrupted ISO or WBFS file can also trigger this error
Step 2 – Check Disk Space
Ensure at least double the ISO size is free (e.g., for a 4.7GB ISO, have 10GB free). Dolphin may create a temporary copy.
Step 3 – Use an Uncompressed ISO
Step 4 – Rebuild, Don’t Patch
If you need to add/replace files larger than the originals, do not use in-place replacement. Instead:
Step 5 – Try a Different Dolphin Version
Some development builds introduce FST writing regressions. Test with: Dolphin may not have permission to modify the NAND files
Real-time scanning tools (like Windows Defender, McAfee, or Bitdefender) sometimes lock files that Dolphin is trying to modify. If an antivirus quarantines or holds a lock on the FST file, the write operation fails.