Yes, I'm having trouble with that error too. The form 3468 instructions say "If applicable, enter your pre-filing registration number..." so I'm thinking it is not required, but I still get the error if I input "Not Applicable". The taxpayer says they don't have an IRS registration number.
Also, when I enter the cost of the solar energy property on form 3468, Part VI, Line 3a, the cost does not flow to the K-1s on the 1065 and 1120S modules in Proseries.
I've been waiting since Thursday for someone to get back to me on this issue. The agents over the phone don't seem to be aware of how to proceed with this form 3468 and gasification issues.
I just sent Intuit a sample file of how the 3468 currently works, with the Line 2a error and project cost data not flowing to 1120S/1065 Schedule K and the shareholder/partner K-1s. Hopefully they are working on fixing it.