In what circumstances can the directors decline a transfer of shares?

Clause 20(1) of Schedule -I:

The directors may decline to register any transfer of shares not being fully paid up shares, to a person of whom they do not approve, and may also decline lo register any transfer of shares on which the company has lien. The directors may suspend the registration of transfer during the fourteen days immediately preceding the ordinary general meetings in each year. The directors may decline to recognize any instrument of transfer or refuse to register such transfer, unless –

a) the instrument of transfer is accompanied by the certificate of share to which it relates; and 

b) Such evidence as the Directors may reasonably require showing the right of the transferor to make the transfer has been furnished.

c) Form 117 is duly filled up.