Here's what would fix it:
Code:
FREESLOT
MT_DEVILSS
S_DEVSPAWN
S_DEVATCK11
S_DEVATCK12
Thing MT_DEVILSS
MapThingNum = 4022
SpawnState = S_DEVSPAWN
SpawnHealth = 8
SeeState = 1806
SeeSound = 127
ReactionTime = 32
AttackSound = 0
PainState = 1840
PainChance = 200
PainSound = 0
MeleeState = S_DEVATCK11
MissileState = 1838
DEATHSTATE = 1846
DEATHSOUND = 0
XDEATHSTATE = 0
SPEED = 7
RADIUS = 1572864
HEIGHT = 2097152
MASS = 100
DAMAGE = 2
ACTIVESOUND = 0
RAISESTATE = 1842
FLAGS = MF_BOSS|MF_SHOOTABLE|MF_NOGRAVITY|MF_FLOAT|MF_SPECIAL
#Devil Super Sonic's spawn state:
STATE S_DEVSPAWN
SPRITENUMBER = 245
SPRITESUBNUMBER = 0
DURATION = 1
NEXT = DEVSPAWN
ACTION None
VAR1 = 0
VAR2 = 0
#Devil Super Sonic charging and firing a bomb ring at the player:
STATE S_DEVATCK11
SPRITENUMBER = 245
SPRITESUBNUMBER = 2
DURATION = 35
NEXT = S_DEVATCK12
ACTION A_PlaySound
VAR1 = 156
VAR2 = 0
STATE S_DEVATCK12
SPRITENUMBER = 245
SPRITESUBNUMBER = 0
DURATION = 15
NEXT = 1835
ACTION A_FireShot
VAR1 = 223
VAR2 = 0
I get no errors with this code.
You also need to put frames in the FREESLOT category.
(Btw, you can also refer to FRAME as STATE, so I just changed that because state is used more)
Maybe a little bit more help: http://wiki.srb2.org/wiki/State