Francis Heaney points out a strange Christmas ornament with the legend "internally grateful". That one seems to be a joke, though it's hard to be sure, but there are many folks out there for whom the same phrase is an eggcorn. This case is an interesting one, since "internally grateful" is well formed and perfectly sensible, but examples like those below seem almost certainly to be based on misconstruing the cliché "eternally grateful":
Posted by Mark Liberman at June 4, 2004 01:45 PM(link) If anyone can solve my problem, or tell me how to tell word to open as readonly (I suspect this may solve the problem) I will be internally grateful.
(link) right now my life is going great thanks to friends & family & all the other people who have helped in my continuing recovery, especially my wife Carol & my son Mark, who I'm internally grateful for all their love & support.
(link) He also states that he is internally grateful to his partners and constituents who worked so hard, so many hours, and who helped make the draft a historic and memorable event.
(link) I am internally grateful and consider it an honor and privilege to be listed among my music peers and heroes
(link) I am internally grateful to have been touched by her love and her spirit.
(link) The Stone Roses really did change my life and for that I am internally grateful.