it is not possible to cancel registered gift deed unilaterally 

2) you need court orders to set aside registered gift deed 

the registered document can be cancelled only by order of the court it cannot be cancelled unilaterally. If cancelled through court or agreement between parties then it would be valid. 

See if done unilateral court won't validate same , rest.the document need to be pursued.

file suit to set aside cancellation of registered gift deed as it was done unilaterally without donee consent 

once the document has been registered it can't be cancelled unless through the process of the court.
May be It was a conditional gift deed, so the violation of the condition by the donee makes the gift deed liable to be cancelled. 

Dear Client,

Registered document cannot be cancelled without court order. What was it - sale deed, gift, settlement deed  ?

Was the cancellation deed signed by both the parties . If so you cannot do anything if not then can file a suit in the civil court to.declare cancellation deed invalid.

take legal proceedings as mentioned herein above 

it cannot be cancelled unilaterally . registrar has no powers to register unilateral deed of cancellation 

Even if it is settlement deed once registered it can be cancelled by the parties mutually or by order of court.

The settlement deed once executed and acted upon can never be cancelled.Your grand father cannot cancel the settlement deed once the properties have been transferred . The Deed which is registered can only be cancelled by the Court since an act on the terms of the deed has taken place.

Cancellation illegal. Deed still valid.

If the registration of the property is made because of the gift and it has certain conditions to the gift to be fulfilled by the donee and and failure of complying the conditions the registration may be cancelled by the doner. 

Dear Sir,

Settlement deed and gift deed cannot be cancelled without the signatures of all the parties concerned.  You can challenge such action before the higher authorities of that department and also approach Civil court to declare your father as owner of the property since cancellation of settlement deed is not binding on your father.

You cannot get the document (settlement deed) registered again, as your grandfather had passed away. Your father has to file a title suit based on intestate succession, at the district court.

To challenge the cancellation deed the time limit is three years only, if it is beyond three years, you may have to give proper reasons to convince the court to seek cancelaltion of the cancellation deed.

Once a property was transferred by a registered  gift or settlement deed, the donor cannot cancel the the said registered deed unilaterally. 

This can be challenged in the court of law, but since the donor is not alive now, the reasons seeking cancelaltion of this cancelaltion deed has to be established with substantial evidence.

If the registered settlement deed was cancelled by a registered cancellation deed, then this can be rectified by filing a suit for cancellaiton of the registered cancelaltion deed and also for declaration of title and for possession if possession of property is not with your father.

Before that you may see the reason shown in the registered cancelaltion deed  for cancelling the settlement deed, if it has any valid reason then you may have to prepare grounds and evidences to nullify the same.

Discuss at length with your advocate on this and proceed

settlement deed

It was a registered settlement deed hence it was easy for the donor to cancel the same by executing a registered cancelaltion deed.
You can follow the procedures of law to get it rectified 

Dear Sir,

Settlement Deed cannot be cancelled unilaterally. You may approach the Court and get necessary favorable orders.