When did they stop eating the Manna?
Rashi and Targum Yonasan: On the fifteenth of Nisan of the fortieth year after leaving Egypt. 1
That being the case, bearing in mind that the Manna began to fall on the fifteenth of Iyar (one month after they left Egypt), how can the Torah state that they ate the Manna for forty years?
Rashi: This teaches us that the 'cakes' that they took out of Egypt (and which they ate from the fifteenth of Nisan until the fifteenth of Iyar) tasted like Manna.
What is the Torah referring to when it writes that they ate the Manna until they came to inhabited country?
Rashi: It means that the Manna stopped falling when they arrived in the land of Sichon and Og on the banks of the River Yarden, before Moshe died. 1
Seforno: When the Pasuk says that the B'nei Yisrael ate the Manna for forty years, it means that they ate only the Manna and no other food. That lasted, the Pasuk is now telling us, until they arrived at inhabited country - the land of Sichon and Og, when they began to eat of the local bread as well. 2
How will we reconcile the phrase which states that they ate the Manna until they came to inhabited country (the land of Sichon and Og) with the previous statement that they ate the Manna for forty years until the fifteenth of Nisan?
Rashi: The former (with reference to after they crossed the Yarden) refers to when the Manna fell for the last time; the latter, to when they actually stopped eating it. 1
Seforno: The former refers to when they last ate only the Manna, the latter, to when they ate the Manna for the last time. 2