Timing of filing Form 5330 for late deposits

[BG5150]

We found out today that there was a 401(k) deferral deposit that was not made at all from 2009.

After the amounts are paid to the plan and the interest allocated, we need to file Form 5330 for the late amount.

From what I understand, I will have to file THREE forms, one for each tax year.

But, the form says that the form is due "by the last day of the 7th month after the end of the tax year of the employer (or other person who must file the form).

So, are the 2009 & 2010 forms LATE?

The instructions say there is a penalty on the unpaid tax. But you might not have to if "you can show that the failure to pay on time was due to reasonable cause."

Is "we didn't know about this until today" a "reasonable cause"?