Ok. Right off hand, you're trying to check a variable that you have not given life to. In this new version all undefined variables start out as 'null'. At the start of your script, you must first check if the variable is null by using the text compare rather than a value compare. Place the check for null at the start of your event.
;This will give your variable a starting value if it had not been instantiated yet.
{check: compare, text, <var.caster.rideflames>, is:equal:null}
{var: caster, rideflames, value, 0}
{endcheck}
Another good idea is just to stop using values for variables that are only used as flags. Use a text variable instead so you wont have to worry about making the above line of code. Values should only be used for math - not flags. Actually, just change you check compares to text. That should fix the problem all together.