I don't know why you are getting that error.
Though I use ULX v2 now (without any of the 1.x releases), I originally used his menus addition/changes with ULX v1.12 and they worked fine.
Did you edit any of the file? If so, delete it and unzip it back into your ulx folder.
Might try upgrading to ulx v1.13, the latest v1, then paste over the ulx_menus.lua also.
Let us know if that works.