I am sorry, willi6868, but it looks like a hardware error. Flash cards do not last forever. I suspect your card is a goner and your data with it. There is a VERY small chance that something might be retrievable but I would not hold my breath.

You can try:

to see if the card's hardware is recognized at all.

I once had a card that suddenly failed. It was an 8GB card. Following the failure, any system I tried it on recognized it as a 32KB card and could not write to it. There was no chance of recovering any data from it. Family pictures from the last two holidays gone just like that.