Deductible loan guarantees are rare animals.  You actually have a client who qualifies?

Loan guarantees. If you guarantee a debt that
becomes worthless, you cannot take a bad debt
deduction for your payments on the debt unless
you can show either that your reason for making
the guarantee was to protect your investment or
that you entered the guarantee transaction with
a profit motive. If you make the guarantee as a
favor to friends and do not receive any consideration
in return, your payments are considered
a gift and you cannot take a deduction.

Are you checking Box C on the Form 8949?  Maybe ProSeries wants you first to complete the required statement:

For each bad debt, attach a statement to
your return that contains:
• A description of the debt, including the
amount, and the date it became due;
• The name of the debtor, and any business
or family relationship between you and the
debtor;
• The efforts you made to collect the debt;
and
• Why you decided the debt was worthless.
For example, you could show that the borrower
has declared bankruptcy, or that legal action
to collect would probably not result in payment
of any part of the debt.