If a person for some reasons forgets or is not able to do Shradhha Paksha of his ancestors, but does lots of Namajapa or chants Hari-nama lots of times in his life everyday, does he still get the ill effects of that omission?
From Om Viṣṇupada A.C. Bhaktivedanta Swami:
According to the rules and regulations of fruitive activities, there is a need to offer periodical food and water to the forefathers of the family. This offering is performed by worship of Viṣṇu, because eating the remnants of food offered to Viṣṇu can deliver one from all kinds of sinful actions. Sometimes the forefathers may be suffering from various types of sinful reactions, and sometimes some of them cannot even acquire a gross material body and are forced to remain in subtle bodies as ghosts. Thus, when remnants of prasādam food are offered to forefathers by descendants, the forefathers are released from ghostly or other kinds of miserable life. Such help rendered to forefathers is a family tradition, and those who are not in devotional life are required to perform such rituals. One who is engaged in the devotional life is not required to perform such actions. Simply by performing devotional service, one can deliver hundreds and thousands of forefathers from all kinds of misery.
It is stated in the Bhāgavatam(11.5.41): "Every human being born in this world is immediately indebted to the demigods, the great sages, ordinary living entities, the family, society, and so on. But a person who surrenders unto the lotus feet of the Lord and engages fully in His service is no longer indebted to anyone. In other words, he has no obligations to fulfill except executing devotional service."