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Recently I just deleted one of my answer in stackoverflow where there was one comment.
After deleting the answer it also show for sometime that we all know but in the comment it still allow us to up to make it useful but as I clicked it it just showed me the message:
If we are not allowed to do then what was the meaning? Why don't it just be removed or make it disable if the answer is deleted.
Just don't show UI for actions that can't be actioned
In general, you are correct, it is a good idea for the UI to give end-users a visual feedback on which actions will be allowed and which actions wouldn't be allowed without having them to click around the interface. If the voting is not allowed, you should see the corresponding parts of the UI grayed out.
However, there are situations when the UI state does not reflect the state of the system. For example, if that deleted answer was by someone else and you did not refresh the interface, the UI wouldn't know that the answer has been deleted. The system needs to be prepared to handle situations such as this one with orange pop-up messages explaining why the action is not allowed.
The orange box code has to be written anyway, but the visual feedback code is optional. The orange box mechanism covers both scenarios (i.e. a deleted entry that looks like a deleted entry, and a deleted entry that does not look like a deleted entry), while the visual feedback covers only the first case. One could argue that using orange boxes alone provides for a unified user experience, so this feedback mechanism is entirely sufficient all by itself.
No voting actions are allowed on deleted posts (except votes to undelete them).
The SO team has not changed the UI to remove the different options, such as the upvote icon on a comment on a deleted answer/question.
It is probably assumed self evident why this is not allowed and is easier to achieve and have a UI not littered with exceptions (when to display icon X and when not to).
