What is MONTANA's TAX #??

Which form are you referring to? If it is a 1099-G from the state of Montana, please see the following:

This year we have seen a number of states issue 1099-G forms that have tax withheld in box 11, but boxes 10a and/or 10b are empty. TurboTax requires that if box 11 has a value, then boxes 10a and 10b must also have entries.

Box 10a is probably the two-letter state code for your state (example: "MI" for Michigan). The filer identification number for box 10b is likely to be the same to the Payer’s TIN on the left side of the form.

If your issue is something else, please come back and tell us.