I got the same issue (not charging) with the same symptoms (red light for ~5 seconds).
problem solved - I changed to a new, "higher quality" usb cable.
(the old cable was 3 years old and has had a hard life)
Looks like the Purity Pro is fussy about it power source.
it stops charging after 5 seconds if it thinks something is wrong.
Yves, thanks for finding a solution, but could you be more specific? I've tried all three usb cables I have (all from nokia sets) and none of them are making any difference.
What constitutes a 'higher quality' usb cable?
Thanks