A 100% owned S Corp. Loaded info for sole owner and software is looking for a second owner. Tried deleting and starting again but no good. What can I do?

You sure you're in an 1120S return and not a partnership 1065?

Review the Schedule K-1 Worksheet.  Make sure there are no stray entries in what should be all blank fields of the Shareholder Information for the second shareholder.  A stray entry in some fields can trigger "Shareholder No 2.  Also, just below the Shareholder Information, make sure the "Total number of K-1s...." is 1 and that the "Total number of K-1s at year end..." is 1.  If it is not you will have to delete the mystery shareholder's K-1.  

1. Page down on the ScheduleK-1 Worksheet for the last shareholder.
2. Use the delete key on each and every field for that shareholder. Delete ALL data for that shareholder.
3. Now go to that shareholder Schedule K-1 itself (should be shown as "Untitled").  Choose the "Remove Schedule K-1" selection from the Forms Menu.
4. If the Schedule K by activity has been used, a dialog box will appear listing this Schedule K-1 untitled as well as the Schedule K-1 by Activity Information form.  Choose the "Remove Listed Forms" button.
5. Go to the Shareholder's Basis Statement (Basis Stmt).  The last one will be shown as "untitled".  Choose the "Remove Basis Stmt" selection from the Forms menu. 
6. If the shareholder stock and loan basis has been maintained, the Basis Information Worksheet will still contain the original information for the deleted shareholder. It must be manually deleted.