oh I'm glad, someone is answering...
So, I don't have the message anymore. Because I thought maybe when I log out, the plug in will come back.
But it was not the case.
But as far as I can remember, it was something like I.G.S. wrote. ".... the update had failed to install." It was a red font and shaded in a light red.
@ Ian: My site is still working. But instead the shop, is there the Home-page
But I will try to take up the idea with the backup plug in. May be it will work. I'll let you know...
Thank you both so much for helping me...