statue of limitation

What is the name of your state? montana
we were audited by the irs in january, 1999 and they forwarded the results to the state of montana and we never hear from the state until yesterday. what is the statue of limitaions the year is 1996 that they are collecting for. we were more than 25% in error. how many years can they go back

You need to consult a MT tax attorney.