Thank you for the response @DianeW777. I believe you have answered my question as to why Schedule U is being created (it looks like Part I is required for all filers now?), but I am still unsure as to why TurboTax thinks I owe a penalty.
The Schedule U form itself is filled out correctly by TurboTax using last year's liability and this year's estimated tax payments, and line 12 (Total underpayment for year) shows a negative balance which, according to the form, means there is no penalty (If the result is zero or less, stop here; you do not owe underpayment interest).
So, I guess I am back to wondering why:
1) TurboTax thinks I owe an underpayment penalty?
2) Why is Schedule U causing an error message in Adobe? (Apologies for the lack of details on this second part. As I mentioned in my original post, I simply get a message that says "An error exists on this page. Acrobat may not display the page correctly. Please contact the person who created the PDF document to correct the problem.")
Thanks for your help! - Don
