There Was An Unhandled Exception Trying To Save Your Rom To Disk |link| -

referenced in the message (found in the same folder as the randomizer) for more technical details like java.io.IOException or finding a clean base ROM [Bug] Issue by 'Randomize (Save)' #771 - GitHub

Getting hit with the message can be a real mood-killer, especially when you’ve just spent time perfectly tuning your randomizer settings. This error usually pops up in the Universal Pokemon Randomizer ZX or similar tools. referenced in the message (found in the same