Hey PSI, I'm making some progress finding the issues... as for the IID error, it dissappears if you remove the events that destroy the Spriter object in question! This tells me its a bug in the Spriter plug when you delete either Spriter objects in general, or perhaps one that doesn't exist in frame (meaning count-0, its already been distroyed but an event tries to destroy one of these Spriter objects that don't currently exist. )
I've also fixed half of the flipping issue, in that if you use the same exact method (xmirror) instead of set scale etc to flip both Spriter objects (flame and player spriter objects), AND always flip both in the same events..IE, whenver you flip the player, immediately flip the flame in the same event, then they always flip properly at the same time!
The remaining problem is the x-coordinate of the flame is still taking one extra frame to update and catch up to the apropriate position.... I've talked to Edgar about this and we'll see if either he can get rid of the 1 frame lag or if I can some up with a decent work-around for you.
Thanks for your patience...the complexity of your project makes trouble-shooting more difficult.
Mike at BrashMonkey