There Was An Unhandled Exception Trying To Save — Your Rom To Disk

: If you have used a tool to reduce the file size of your ROM (trimming), the randomizer may fail to save. Use a completely unmodified, clean ROM instead.

It sounds simple, but if your hard drive is full, the "unhandled exception" will trigger.

Antivirus software sometimes flags emulator files as suspicious and prevents them from writing to the disk.