99999 is used when you cant find a Business Code that describes your business.....what type of business do you have?
Is my problem due to the fact that Premier version doesn't handle schedule C?
Someone else will have to help you with the logistics of "where" to find the place to change the code....Premier should handle a C-EZ, but probably not a full Sch C. If a full Sch C is required, the program should prompt you to upgrade.
This looks like your options for choosing a code though.
<a rel="nofollow" target="_blank" href="http://www.naics.com/naics-code-description/?code=621610">http://www.naics.com/naics-code-description/?code=621610</a>