p. 241
तनः चिरंतन इत्यर्थः ।संसारानर्थहेतुत्वेन वेदाध्ययनतदर्थनिश्चयतदनुष्ठानानि न कर्तव्यानीत्यर्थः ॥
In plain words
The ending '-tana' here means 'from of old' — ancient, going all the way back. And the sense of the line is this: because they are what causes the misery of saṃsāra, reciting the Veda, settling what it means, and carrying out what it prescribes are not to be undertaken. That is the meaning.
Close to the Sanskrit
'-tana' — 'ancient, from of old' is the meaning. Because of being the cause of the calamity that is saṃsāra, the study of the Veda, the ascertainment of its meaning, and the performance of that are not to be done — such is the meaning.