What is going on here?
From what I can make out (from a quick refresher look-see in GTR4), Ptolemy was an OK guy when, back in Barbour's time it was thought he supported the view that Cyrus' first year was 536 BCE (+ 70 = 606 BCE). Then when Russell realized that this wasn't the case, that Ptolemy supported 538/7 BCE as his first year and also 587 BCE as the date of Jerusalem's destruction, then Ptolemy was no longer an OK guy.
Add to that R.R. Newton's controversial book "The Crime of Claudius Ptolemy" ...
w77 12/15 p. 747 Insight on the News
In its comments on Newton's book, "Scientific American" magazine notes: "Ptolemy's forgery may have extended to inventing the length of reigns of Babylonian kings. Since much modern reconstruction of Babylonian chronology has been based on a list of kings that Ptolemy used to pinpoint the dates of alleged Babylonian observations, according to Newton 'all relevant chronology must now be reviewed and all dependence upon Ptolemy's [king] list must be removed.'"-October 1977, p. 80.
... well, we can join the dots.