The folder is too full is all it is. If you set your rights to rw NPCS/*a*, you'll see only those files in there that have an a in them and it won't crash. You do the same with e,i,o,u and it will subdivide it. Can also be done with numbers 0 through 9 if you've used those in the names. Eliminate any that you no longer use and you will reduce the folder size so it won't crash you.