Hi, for some reason it seems like it thinks you need the Delete Rename window (you have either Show Delete or Show Rename enabled in the plugin parameters) but that window doesn't seem to have gotten created, so it is undefined and when it goes to activate that window it crashes.
I did a little investigation and was not able to reproduce this myself, so I am wondering if there is some potential plugin conflict here that is causing that window to not get created. Could you try on your end to turn non-CGMZ plugins OFF temporarily and see if the issue no longer occurs? If so, it would point toward a plugin conflict. If you are still able to reproduce with [CGMZ] plugins only, can you let me know your Save File plugin settings?