I was recently told that one character can only make 1 free action a turn. If this is true, then my KC Flash (given that he has clear LoF to the character and is within 10 squares away) cannot outwit your defense then hypersonic you. HS grants a free action to make a close or range combat attack. I was sure that I could outwit and then Hypersonic Speed. If not, I will not like Flash nearly as much.

That is incorrect. Your characters can take any number of free actions during a turn. They are free, after all...

What your source may have been misinterpreting is that many free action come with a 'once-a-turn' clause (like Outwit or Perplex). If it doesn't specify 'only per turn', though, you can use it as much as you want (Nanobots is the first thing that springs to mind).

Thank goodness. I was told I couldn't nanobots 2 times in one turn, then perplex up my range to shoot. Booya!

Yup, that would be perfectly fine. If someone is still giving you a hard time about this, refer them to this passage in the rule book (page 16, under 'Free Actions'):

A character or force may take any number of free actions in a turn, but only as their powers and team abilities dictate. A free action may be used to perform a close combat, ranged combat, move, or power action; in each case, the description of the free action will indicate what other type of action may be used.