In RMFRP A-9.17.3 we read that we can try one time per lvl (of course for the same target), but for the other we can read, I think is really one time per rank in list (if you fail you can only try again if develop a new rank).
This (limited number of attemps) is clear for some spells, as 'remove curse', but I suppose that this could be used as general rule for all attack spells, for example when you try to 'unsymbol' is the same, 'dispell magic', or even a simple 'sleep' could have this limit to evade the infinite attemps until it works.
This could be very important for low level characters, for example, in first level, a sorcerer could try a 'sleep V' spell once, twice or 3 times depending on their ranks, but if it fails, that can be a serious problem.