So when i was playing my SR Flash, I missed an attack roll when using HSS. I then used probability to re roll the die, but my opponent said that you couldnt use prob in HSS. He wasnt completely sure about, so thats what im wondering. Can Prob be used in the middle of HSS?

Yes. I'd say to him "show me where it says you can't". It's not an action, so it can be used after any roll made by a figure.

Well, it wasnt sure. It was a friendly game so it didnt really matter.

He did bring up that you can prob a character when its carrying another character ( the one with the probabilty) because the carried character is "off the board" until the movement ends.

The confusion may be coming from the fact that a charachter being carried during HSS is considered to be off the board until movement ends, and can't use any of it's powers.

For example: Superman carries Sandman during a HSS attack and misses. Since Sandman is considered "off the board", there's no way for him to draw line of fire to Supes for his PC. Anyone not being carried can use thier powers & abilites as normal. Same goes for Enhancement & PD/Hydra team abilities.

*edit* Aparently you got that one, though. Curse my slow fingers.

A character using HSS can use PC on itself since the character is on the board and has a well-defined location. Your opponent might have been confused because if a character with PC is being carried by another character with HSS (but not PC), then the carried character cannot use PC to assist the character with HSS because the carried character is not considered to be on the board while carried and does not have a well-defined location.

edit: in other words, "what BlueRabbit said".