It shall be unlawful for any beneficial owner, director or officer, directly or indirectly, to sell any equity security of such company if the person selling the security or his principal does not own the security sold, or if owning the security, does not deliver it against such sale within twenty days thereafter, or does not within five days after such sale deposit it in the mails or other usual channels of transportation; but no person shall be deemed to have violated this section if he proves that notwithstanding the exercise of good faith he was unable to make such delivery or deposit within such time, or that to do so would cause undue inconvenience or expense.