YOU SAID:

not allowed meaning cannot as that is impossible and mean

INTO JAPANESE

許可されていないことを意味することはできません。

BACK INTO ENGLISH

It cannot mean that it is not allowed.

INTO JAPANESE

許可されていないということはできません。

BACK INTO ENGLISH

It cannot be said that it is not allowed.

INTO JAPANESE

許されないとは言い切れません。

BACK INTO ENGLISH

It cannot be said that it is not allowed.