What BandiKoot said, if you want to see what else might cause an error, get FNVEdit, the program runs all the active esps and esms and if there's an error it will tell you and tell you what esm is needed to run.
It could be some mods you had used or worked with stuff from Project Nevada, see if any versions of your mods use it, but that's just a guess, your best bet is to use LOOT or FNVEdit