On what grounds does one bring a Korban Asham Taluy?
Rashi, Seforno and Rashbam: For committed an act which is a Safek Kares, 1 b'Shogeg.
Seforno: For not being careful not to enter into a Safek.
For example, if he inadvertently ate one of two pieces of fat that were lying in front of him, one Chelev (of which he was unaware - Rashbam), one Shuman, and he is not sure which one he ate, he brings an Asham Taluy.
What can we learn from the fact that the Torah punishes even someone who is not aware of the circumstances that create the sin that he is performing?
The very thought should serve to instill in a person Yir'as Shamayim.
R. Yossi goes one step further: See how many deaths Adam ha'Rishon brought upon himself and upon the world, when he transgressed the single Mitzvah that he was commanded. Now, bearing in mind that the Hashem's Midah of goodness exceeds that of punishment, imagine how many merits someone who sits and desists from eating Pigul and Nosar, or who fasts on Yom Kipur will bring upon himself and upon his descendents until the end of time. R. Akiva adds - Bearing in mind that, based on the Pasuk in Parshas Shoftim, Chazal declare a third (superfluous) Eid Zomeim guilty of the death-penalty, for participating in the sin of testifying falsely, imagine how much reward is forthcoming to someone who participates in a D'var Mitzvah. And finally, R. Elazar ben Azarya points out that if the Torah issues a blessing upon someone who performs the Mitzvah of Shichechah - by forgetting a sheaf which a poor man subsequently gathers, then by the same token, someone who drops a Sela and a poor man finds it, will earn a Divine blessing.
Rashi writes that Asham Taluy shields him from punishment until he discovers that he sinned. Why do punishments come for a Safek sin, and not for a Vadai?
Moshav Zekenim (1): This is so one will examine his deeds, and if he finds that he sinned, he will repent. However, punishments do not come on a Rasha, in order to derive him from the world [to come] if he will not repent.
For which Safek Aveiros is Asham Taluy brought?
Moshav Zekenim: Kerisus 6:3 teaches that it is only for an Aveirah that has Kares for Mezid and a fixed Chatas for Shogeg. This excludes a Safek about Me'ilah, which has no Kares, and Safek Tum'as Mikdash, which is only Oleh v'Yored b'Shogeg.