Help only helps if you read it...the previous poster let you know that the "/" in the reset section of your castsequence was incorrect, while he simply omitted everything after the slash you could have gone and found that you need a comma thereby making your macro

Code:
/castsequence [target=targettarget,harm] reset=6,target Lava Burst,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,
This macro will work and attempt to cast LvB everytime because you are changing targets all the time with the FTL method. This is the reason I believe the target parameter was omitted. So now your macro would be

Code:
/castsequence [target=targettarget,harm] reset=6 Lava Burst,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,
Which will work just fine if you gain a friendly target just before casting and that friendly target has some harmful target selected. The problem is your assist macro working in conjunction with this macro. Assist does not change or modify your target as far as the targettarget is concerned, it simply makes the next spell target the target of the person you have assisted. So now we have looked at whats happening and discovered why

Code:
/castsequence reset=6 lava burst,,,,,,,,,,,,,,,,,,,,
Works, when

Code:
/castsequence [target=targettarget,harm] reset=6/target Lava Burst,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,
does not.

If you want to use the majority of the macros you have posted simply change the

MACRO 16777233 "Target" INV_Misc_QuestionMark
/assist [mod:ctrl,mod:alt,nomod:shift,target=Garey] [mod:alt,mod:shift,nomod:ctrl,target=Garew] [mod:ctrl,mod:alt,mod:shift,target=Garev] [mod:ctrl,nomod:alt,nomod:shift,target=Gareu]
END

to

MACRO 16777233 "Target" INV_Misc_QuestionMark
/target [mod:ctrl,mod:alt,nomod:shift,target=Garey] [mod:alt,mod:shift,nomod:ctrl,target=Garew] [mod:ctrl,mod:alt,mod:shift,target=Garev] [mod:ctrl,nomod:alt,nomod:shift,target=Gareu]
END

then make sure you correct the "/" problem in your castsequence, and tada FTL works with castsequence...