What Mac version do you work on?
Also tell us the Acrobat version?
If you obey the error message,were there any changes made to the document?
The Mac version is OS X El Capitan - version 10.11.3 and Adobe Acrobat XI Pro. If I obey the error message, only the first two pages become fillable, otherwise the rest of the pages do not become editable/fillable. Thanks,
Please check if Acrobat is updated to the latest patch.
Launch Acrobat>Help>Check for Updates
Acrobat is up to date.
Was there ever an answer to this?
Has there been any answers to this.
Adobe Acrobat was unable to make this document accessible because of the following error:
Knowledge source failed. <Gather Form Data> 
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Sorry for the delay in response.
Could you let us know if you are getting this error when trying preparing form in Acrobat? If yes, try printing the form to Adobe PDF as suggested by Adelaney in the following link and check if that helps:
Or try the suggestion posted by Dwhit in the thread below: