1. Make sure you do not make any entry under General > Client Information for the spouse's SSN;
2. Under General > Misc. Info./Direct Deposit, click on the Miscellaneous tab; and
3. Scroll down to the line for Spouse is a nonresident and does not have an SSN/ITIN (MFS Only) and check the box.

If this solves your problem, you may consider marking this the solution to help others who have similar questions.