What to do?
Frankly, I never saw anyone shoot the same card "live" in a Canon, and pull it, and put that card in a Nikon....and shoot more.
My only thought is to put the card in the reader, which should come up in Windows Explorer as a Drive with a letter.
I would try to navigate to the Canon folder that contains the Raw image that will not come out. Open a second copy of Windows Explorer and find your destination folder.
See if you can copy/paste that recalcitrant file from the card to the Hard Drive.
If that doesn't work, then you can try one of those image recovery apps. I have one that recovers images from cards that have been formatted.
I would try to recover the files.
No Success?
I would Format the card and try that recovery app again.
There are a number of them offered FREE on the internet, but if you want a copy of what I use, "Digital Image Recovery", holler with Email address, and I'll send it.
It's pretty small.
Fred