Some older versions of Dolphin (pre-5.0) had unstable ISO rebuilding code. Certain development builds (beta or nightly) might also introduce temporary regressions in IOSFS handling.
The error message (and its closely related variant "IOS_FS: Failed to rename temporary FST file") is caused by Dolphin Emulator being blocked from updating or creating filesystem files in its virtual Wii NAND directory. This issue prevents the emulated Wii Input/Output System (IOS) from properly writing its File System Table (FST), causing frequent error pop-ups when starting or stopping games.
If you are still hitting a wall with this error, let me know: dolphin iosfs failed to write new fst
Background — what the components do
If you only experience this error when launching Dolphin via a gaming frontend like LaunchBox or Big Box, the issue is likely due to mismatched administrative rights. Check the properties of your frontend application. Some older versions of Dolphin (pre-5
Windows often blocks applications from writing data to the C:\Program Files or C:\Users directories without explicit permission. Right-click the shortcut or executable file. Select Properties from the context menu. Navigate to the Compatibility tab. Check the box next to Run this program as an administrator . Click Apply and then OK . Launch the emulator and try again. 2. Disable Controlled Folder Access
Right-click the folder and select Properties . This issue prevents the emulated Wii Input/Output System
For more technical details on NAND emulation, you can check the Dolphin Emulator Wiki or browse community solutions on the Dolphin Emulator Reddit setting antivirus exclusions for a specific program?
) may be set to "Read-only," preventing the creation of new FST (File System Table) files. NAND Path Configuration