It appears that this error is related to the date of birth. I opened an existing client return, previously filed with only basic information like W-2 wages, investment income, and itemized deductions and the diagnostic error was not present. However, once I modified the date of birth to indicate that the client is 70 1/2 years old, diagnostic reference #55316 appeared. Even after removing the W-2 information, the error persisted. I even created a new tax return, entered just the basic personal details, and as soon as I set the date of birth to reflect an age of 70 1/2, the error showed up on the otherwise blank return. This strongly suggests that it's a bug.