"You are not going to be able to ... " versus "you can't ..." [closed]

When talking about physical or other external (im)possibility in the future, they are synonymous:

   "You can't get in to the building tomorrow"
   "You are not going to be able to get into the building tomorrow"

But if the issue is of permission, you would not normally say

"You are not going to be able to go tomorrow" 

unless perhaps you mean that somebody who has authority to give you permission has not yet made a decision but you think that tomorrow they will forbid you to go.

Since "you are not going to be able to" has a future feel to it, it also cannot be used for a an impossibility or prohibition right now:

"You can't do that!"

Yes, using "you can't..." doesn't imply any reason for what's keeping you from doing something. It might be something that you are clearly able to do, but should avoid for some other reason.

The expression "you can't..." can also be used as a request to keep someone from doing something, in that case the person is always able to do that action, or there would be no point in the request.