Printing Errors or Lights & Stuck Print Jobs

Dear HP Community,

Please help me fix the following printer 'software’ problem.

< BACKGROUND >

 1. Bought this 'all-in-one' 14 months ago at an U.S. 'Office Depot' store.

 2. Mostly used w/ Mac (OS X.9) &  PC (XP) to 'scan’, and Mac to 'print'.

 3. Product only printed 100 B&W pages and 24 color pages since new.

 4. Today tried (for 1st time) to print (1-page) Mac “Pages” document,

       on “US Letter” sized paper - with “US Letter” sized copy paper in

       printer’s (‘default’ and only) "Tray 1" tray.

 5. In the “Pages” ‘Document>“Printer & Paper Size”’ control box,

       I chose “HP Officejet Pro 8720” & “US Letter”.

 6. Clicked on "Pages" toolbar ‘File > Page Setup…’ buttons, which

       opened a small window where I set these variables’ values:
         Settings: “Page Attributes”
         Format for: “HP Officejet Pro 8720”
         Paper Size: “US Letter”

           (from sub-list of: “Index card Letter 8.5x11 in.”,

                                              “US Letter”, and

                                              “Borderless 8.5x11 in.”)
         Orientation: “Portrait”
         Scale: “100%”

 7. Then clicked on window's ‘Settings: “Page Attributes” button,
       next on its just-opened “Save as Default” option, and finally

       clicking “OK” button to ‘lock in’ these changes & close window.

< PROBLEM >

 8. When re-open “Page’s” ‘File > Page Setup…’, to verify changes are

       indeed “locked in”, I find they are not! My (“US Letter” ‘Paper Size’

       selection ALWAYS gets changed to “Index card Letter 8.5x11 in.”

 9. Thus, when I open “Page’s” ‘File > Print…’ command, and click “Print”

      (to have document printed on its “US Letter” sized paper), an error

      message icon immediately leaps from Mac’s desktop tray to announce:

       “Paper Size Error:

        Specified custom paper size is not supported in selected tray. < OK >”

         and lists its “Stopped - ‘Filter’ failed, 1 page” error message.

10. This is another “HAL 9000, NOMAD, CATCH-22” problem, in which:
    a) the printer first forcefully changes the correct “Paper Size” selection

         to an incorrect selection, and then (logically?!)
    b) refuses to print, since this incorrect selection does not match

         the correct ‘Paper Size’ paper stored in its default tray.

< RESOLUTION? >

 I have made numerous attempts to circumvent this problem, including:
   a) trying other ‘Paper Size’ options;
   b) turning OfficeJet’s “Settings > Setup > Tray & Paper Management >

         Override A4/Letter” switch on “On” and “Off”; and
   c) choosing (but not printing with) “OfficeJet 8270 (Fax)” as “printer”,

        (for which “US Letter” ‘Paper Size’ is accepted),

 but none of these attempts have enabled me to print my ‘document’.

 However, if I:

   d) run the ‘test print’ diagnostic,

 the printer prints out a ‘test print page’ just fine)!

 I am not a ‘happy camper’! A few weeks ago I spent hours (and $120)

 to install new ink cartridges, and now find myself again spending

 more hours just to print a 1-page document!! (This product needs to

 devote a fraction of its “verifying genuine HP ink is being used”

 ’ smarts’ on making things easier for the user!)

 Any help in resolving this problem would be most appreciated.

 Thank you for your kind consideration.

 Sincerely,

 My-oh-my