There Was An Unhandled Exception Trying To Save Your Rom To Disk · Confirmed & Deluxe

To prevent this error in future versions:

Portable versions run entirely from one folder without writing to system locations.
Example: RetroArch Portable for Windows. Extract to a folder like D:\RetroArch, and all saves stay inside that folder. To prevent this error in future versions: Portable

Emulators store save files in specific folders. If that path contains: To prevent this error in future versions: Portable

...the save operation will fail.

try
File.WriteAllBytes(savePath, romData);
catch (Exception ex) when (ex is IOException or UnauthorizedAccessException)
ShowUserFriendlyMessage($"Cannot save ROM: ex.Message");
    LogError(ex);