It's a way to prevent users from submitting too many short, meaningless responses at warped speed as a way of "Xper grubbing". If you wait just a short time, it'll let you submit the opinion. You do not ever lose any Xper points when you see this message.
No, you shouldn't lose any Xper for something like that.
I haven't heard of this happening before, but sometimes when you are clicking and sending pages too quickly, sites will warn you to slow down a little bit... maybe that's what happened here? There should be no limit to how many questions you can answer. (On the other hand, there are some limits to how many questions you can ask.)
I once had that happen after answering only 4 questions but I left short one sentence answers to the questions and I typed them up in about 40 seconds each so I think it is not how many questions you answer but how much or little time yo spend on each one.