• Federally Declared Disasters: If you were affected, you may have extra time to claim a refund on an amended return.
• Combat Zone/Contingency Operation: Time limits are extended for taxpayers serving in these areas, including special rules for hospitalization.
• Worthless Securities or Bad Debts: Claims involving these can often be made beyond the 3-year limit.
• Foreign Tax Credit: Specific rules allow for a longer period to amend to claim a foreign tax credit or deduction.
• Net Operating Loss (NOL) Carryback: If a loss in a later year is carried back to an earlier year, that earlier return can be amended. 
   

• Two-Year Rule: You can always file an amendment within two years from the date you paid the tax, even if the 3-year deadline has passed.
• Audit Status: If your tax return is under IRS examination, you may reach an agreement to amend, even if it is beyond 3 years.
• No Time Limit: If you never filed a tax return, the IRS has no time limit to assess taxes, and in certain cases of fraud, the statute of limitations remains open indefinitely. 

I'd contact ProSeries and see if they still offer it. I have copies but they're on floppy disks......