Sometimes I can't do any posting. Why?

Question

[You do not have permission to perform this operation] it says this in red in a red box

It's not now but it did and I had my correct e-mail address and I wasn't ban.

Answer 1

It was because you were new,tem ban,and the negative points you had.It goes away after a certain amount of time.

See here for more info.

Answer 2

If that message came up when you tried to post an answer, then it means you were banned. I'm 99% sure there is no other reason for that to come up for posting.

If you were doing something else like voting, flagging etc and didn't have enough points then it might come up then, if you don't have enough rep. But then the buttons shouldn't appear if you don't have enough points for them.