For anybody interested, the corruption seemed to be because the card is not 100% compatible with vems.
Card logged fine for over a year, but decided to erase all logs and start fresh.
I think the Erase command didn't work properly. It got rid of the files but didn't "erase" the card.
To fix it, I did a "long format" in windows (FAT32) then removing the system file format, then in Vems tun logging off, Erase , then turn logging on again.
I don't know if all these steps are necessary, it's just how I did it.
I have Win10. to remove the file system I ran the command prompt window in administrator mode, then used diskpart and clean commands.