SB 10.45.13

āha cāsmān mahā-rāja
 prajāś cājñaptum arhasi
yayāti-śāpād yadubhir
 nāsitavyaṁ nṛpāsane
Synonyms: 
āha — He (Lord Kṛṣṇa) said; ca — and; asmān — Us; mahā-rāja — O great King; prajāḥ — your subjects; ca — also; ājñaptum arhasi — please command; yayāti — by the ancient King Yayāti; śāpāt — because of the curse; yadubhiḥ — the Yadus; na āsitavyam — should not sit; nṛpa — royal; āsane — on the throne.
Translation: 
The Lord told him: O mighty King, We are your subjects, so please command Us. Indeed, because of the curse of Yayāti, no Yadu may sit on the royal throne.
Purport: 

Ugrasena might have told the Lord, “My dear Lord, it is actually You who should sit on the throne.” Anticipating this statement, Lord Kṛṣṇa told Ugrasena that because of Yayāti’s ancient curse, princes in the Yadu dynasty could technically not sit on the royal throne, and therefore Kṛṣṇa and Balarāma were disqualified. Of course, Ugrasena also could be considered part of the Yadu dynasty, but by the order of the Lord he could sit on the royal throne. In conclusion, these were all pastimes the Supreme Lord enjoyed as He played the part of a human being.