As an update-(a "mongo smart" moment on my behalf.)
I was driving home and had a 2cent idea.
Using the advice given here- that the card was experiencing difficulty overwriting itself because it was getting full- and it was,
I reformatted the card.
Works perfectly.
Thanks all.
And I will backup to HD on a much more frequent basis now!
Having to buy new card decision averted...As I am sure you will all rest easier tonight knowing this!
