Put in disk in 360. Play Playonline viewer, but screen goes black, and says cannot read disk, need to clean or restart. I did this several times and same result.

I had this problem recently. What happened was you closed the game without logging out of Playonline. The long shut down I call it. This corrupts the FFXI data on your HDD. And since FFXI does not appear in the memory you have to format your HDD and redownload. I can guarantee if you put the disc in your xbox with no HDD that it will read or even place it in an xbox with a HDD that has never had FFXI.

XBox FFXI powered down incorrectly (loss of power or Xbox freeze ect)
I had this problem and finally called XBox support.
Put any music CD into your XBox. Rip the CD to your hard drive.
Go to your music library and play the CD from the HDD. While the music is playing put in the FFXI dics into your XBox the game should load up . . . Its the stupidest thing I have ever heard but it works.

Check to see if there are any scratches or laser burn marks on the discs. Scratches or marks on discs will render the game discs unplayable or will freeze the game and will often show a message stating “Disc Read Error”. Best remedy for starters is to clean the discs and make sure there are no scratches or marks left on the play-side of the discs.
Laser burn, looks like complete or partial circular scratches around your disc, also known as “the ring of death”. This occurs to discs when the games console has been moved whilst playing, from an upright to a horizontal position or vice versa or simply knocked against or the wires may have been just tripped upon. Discs are then impaired by a ring of laser burn, which is a circular scratch into the disc. Some home remedies may help with very light scratches on some discs but professional disc repair services is normally rerquired to restore disc laser burn damage back to "As Good As New Condition".

For further help on Xbox & Xbox 360 disc repairs or to get discs professionally repaired, visit:

www.discREPAIR.ie

Check the More Info Section & FAQ section for more details on disc repairs.

Send your discs off to this Disc Repair Service and the discs shall be sent back as good as new.