PDF/A Confusing Error Message alongside a Confirmation of Converstion

I get an error message in some documents as follows:

“The document has been saved, however, it could not be converted according the selected standar profile: Convert to PDF/A.  Please use Preflight with the profile “Convert to PDF/A” in order to identify those properties of the document which prevent it from being compliant to this profile.”

However, there is a blue ribbon across the top of the file that says

“This file claims compliance with the PDF/A standard and has been opened read-only to prevent modification.”  I'm guessing it is compliant.  I can reopen the document and it says again “This file claims compliance with the PDF/A standard and has been opened read-only to prevent modification.”  So why do I get that error message.

Thank you,

Pat