You have an error someplace in the new list you switched to. You'll keep getting it on startup because Emulaxian is trying to go to that same list when you restart it.
You didn't say what kind of list, so there are two possibilities here - a broken game list or a broken selection set. To get back to a clean starting configuration, try the following:
Check the fewhichselset.cfg file in the cfg folder and, if necessary, edit its contents so it contains the name of a known-good selection set. If you only selected a new game list, you probably don't need to change this.
Check the fe***list.cfg file located in the cfg\selsets folder, where *** is the name of your selection set. For example, if I'm using the selection set named fpsdemo2, I will check the file named fefpsdemo2list.cfg. In there, you'll find the name of the current game list. Change it to a known good list name, and change the last number to the number of the game list in the fe***.cfg file. For example, it might look like this if I wanted Emulaxian to use the Sports gamelist on startup, and Sports was the 16th game list in my selection set:
Sports|1.0000|16.0000|
This should get you back to a starting config that works. If it was a game list causing the problem, try comparing the bad one to the known good one. Same thing for the associated selection set. Most likely, it's a glitch in the fe***.cfg file in the selsets folder. Check that every game list entry in the numbered section has a corresponding entry in the next section. Make sure the numbers are in numerical order. Peter has also said the front end is case sensitive, so to be safe, make sure all the names match case-wise.