Does the Rashash have a good proof against Reincarnation?

[edu]

81 minutes into a parsha lecture of Rabbi Hershel Schachter on Ki Tavo
http://www.yutorah.org/lectures/lecture.cfm/763991/Rabbi_Ezra_Schwartz/Parsha_Shiur_-_Ki_Tavo_5771
Rabbi Schachter brings up a comment of the Rashash (I think that's an abbreviation for Rabbi Shmuel Straussen) on reincarnation. Namely, Rashash comments on Baba Metzia page 107, that the Gemara's statement there seems to be a slight proof against reincarnation.
One of the explanation offered by the gemara in Baba Metzia to the Biblical verse, "Blessed are you when you arrive and Blessed are you when you leave", is:
"that your leaving this world should be like your entrance to this world. Just as your entrance to this world is without sin, so should your exit into this world be without sin".
Rabbi Schachter, then spells out what is the proof of the Rashash. He says that according to the doctrine of reincarnation, a sinner is sometimes sent back into this world to live a new life, to correct the sins that he did in a previous life. Now if this is so, why does the Gemara say that your entrance into this world is without sin?
There may or may not be a rebuttal to this proof, so I would like your feedback.

In any case, Rabbi Schachter ends off the discussion, based on a book called Ohr Hashem, that Belief in Reincarnation is an optional belief in Judaism. That is to say you are not required to believe it and you are not required to disbelieve in it. The fact that Rabbi Schachter ends off with the statement that Reincarnation is an optional belief, somewhat indicates that he might have found a way to answer the Rashash. In his lecture he did not say what possible rebuttal can be made.

[Kahane-Was-Right BT]

Rashash, as in the kabbalist who expounded upon the kabbalah of the Ari?

Or a different "Rashash" ?

Never would have imagined the former would doubt reincarnation for a second since lots of the kabalah is built on that.

[edu]

To quote wikipedia

Rashash (רש"ש) is a Hebrew acronym that refers to either of the two following rabbis:

Shalom Sharabi, Yemenite Halakhist and Kabbalist
Samuel Strashun, Lithuanian Talmudist

I was referring to the second Rashash (although Wikipedia spells his name in english slightly different than my spelling).

[Tag-MehirTzedek]

Rashash, as in the kabbalist who expounded upon the kabbalah of the Ari?

Or a different "Rashash" ?

Never would have imagined the former would doubt reincarnation for a second since lots of the kabalah is built on that.

 I think he even writes about it. (I read once).