Wow. This is totally weird. I was just today having the exact same problem as a result of doing the exact same thing you are doing. In my case I was using ent_morph to toggle through sky models (and I also tried the ent_purge / ent_create method resulting in the "nexus too small" error. FYI: I changed the nexus value in WED and it didn't help.

Can anyone help us here??