Solved
Schedule D-1 is required to show income for installment sales made in PA. I have seen online and experienced with other tax preparation software that returns that include schedule D-1 cannot be e-filed and must be mailed in.
I checked forms availability here and see the D1 is eligible for e-filing in both online and desktop versions.
Enter your E-mail address. We'll send you an e-mail with instructions to reset your password.