I had a photo session and viewed all the photos afterward on my camera, a Canon 6D. The next day I inserted the card into a card reader and my iMac and attempted to import the photos into Lightroom. There were no previews available and when I clicked on import it said that the files weren't supported in Lightroom. I tried again on my Macbook Pro and the same thing happened. I had to schedule a reshoot.
Today I used two different cards, taking photos around my house and making sure all was ok before my reshoot tomorrow. The same thing is happening - three different cards now, two different cameras and two different computers. I have even updated Lightroom. What could be causing this? I am at a complete loss and I don't know what to do
Which Version of Lightroom-6 ?
Which model of the Canon 6D ?
eg. You need minimum v6.12 for the EOS 6D Mark II
I have even updated Lightroom.
Post a screen-clip of the top few lines in the report- Menu > Help > System Info
I have a 6D (not a Mark II) and have CC Photoshop Lightroom 2015.14
As a CC subscriber you can upgrade & update to LR -Classic-CC v7.3 (if your iMac OS allows it- see link below)
I suggest you Upgrade from the CC Desktop App, and also reset your Preferences file.