The Schedule M-2 on the 1120-S is your accumulated adjustments account (AAA).
This is not the same as retained earnings; due to book tax differences.
If you are saying the error only impacts your balance sheet, then I would not worry about it.
If you are saying that the error impacted the income side, and should have been run through AAA, then that does most likely require amending the 1120-S and K-1's and shareholder individual tax returns.
*A reminder that posts in a forum such as this do not constitute tax advice.
Also keep in mind the date of replies, as tax law changes.
