"He has to enter."

Translation: Il doit entrer.

[AnjumPerve2]

What is wrong with "il faut entrer"

[LumiOui]

I wonder the same

[Gregg924411]

Moi aussi.

[RobynCooga]

Il faut qu'il entrer?

[MiriShamir]

"Il faut entrer" not accepted, and
"Il ne faut pas entrer" is ok. Why?