tax preparer mistake
Can a client sue you for an inaccurate return when there was no fraud involved? can they force you to reimburse them?
Can a client sue you for an inaccurate return when there was no fraud involved? can they force you to reimburse them?

This is America ------ anybody can sue anybody else ----------- it's just a matter of who comes out the winner. As far as reimbursement goes, they legally owed the tax whether you did the return correctly or not. If it is a preparer screwup, many preparers will often pay the penalties and interest.
What did you do wrong and how big are the dollars?
I neglected to check the box active participant on sched K-1, so it reported a loss when it shoul not have.

Hardly sounds like a death penalty case to me.

As IRMN stated in his previous response you may want to offer to pay or reimburse any penalites and interest to the taxpayer

In my experience, if you amend the return as a freebie, offer to pay any penalties, and write a groveling letter to the IRS requesting they waive the penalty because it was your mistake and you're going to pay the penalty if the IRS doesn't waive it, the end result is generally no penalty and a non-litigious client.
In my experience, if the IRS catches it first, you've got more exposure. (In the case I'm thinking of, malpractice coverage paid out for the fees to the CPA who handled the audit triggered by the error, penalties, and maybe interest. But malpractice insurance generally will pay out for reasonable expenses, to avoid the cost of litigation.)

Sure he can sue you. IRMN understated the truth of the situation: This is America -------- everybody does sue everybody else. But this REALLY doesn't sound like a candidate for a lawsuit, unless there was already bad blood between you or something. My policy is, when it's my mistake, I pay both penalty and interest ---- UNLESS it's a client I'd just as soon be rid of. Then I only pay the interest.
What damages, other than P&I, is he going to be able to prove? I don't think any court would force you to reimburse taxes that he legitimately owed.
And one last thing: Failure to check the active participant box should have the opposite effect than what you stated, I believe. It should disallow the deduction of an otherwise allowed Passive Activity Loss.
I got burned on this, did not check the box on an S Corp K-1 and it defaulted to passive. Any idea on this logic? I would think the majority of the S K-1's are active and you should have to check the box to make it passive...