The latest Tanks test produced several of these:

runtime error: Cannot create objects of type /obj/mod/security_system.
proc name: DetermineBuildList (/mob/tank/proc/DetermineBuildList)
source file: mobs.dm,417
usr: Sorcer123 (/mob/tank)
src: Sorcer123 (/mob/tank)
call stack:
Sorcer123 (/mob/tank): DetermineBuildList()
Sorcer123 (/mob/tank): build type(Modifications (/obj/buildtype/Modifications))

The type path is valid, and it works fine usually. Every once in a while, it just spits out this error with no apparent reason.

It gave the same error two weeks ago for a couple over /obj/mods, but I was so caught up in the holidays that I didn't report it.