I had a bit of time this evening to mess around with this.
I removed the xlights_rgbeffects.xml file & xlights works again except all my work with the models was gone.
I then opened the xlights_rgbeffects.xml file in wordpad & deleted the model I was working on when it crashed, resaved & my models are back.

Here is the backtrace & troubled xlights_rgbeffects.xml file for you to have a look at. Maybe theres something you can do with it so that if someone else screws up the model parameters it will spit out an error message instead.

BTW the bad model name was se1