While David's comments are certainly valid - as in changes to the file/drive properties, this issue seems to be something specific to 7.1.713 and using catalogs. I've already made mention of this issue here on this forum where, while using C1, thumb images of image files on external storage media fail to appear when that storage media is not attached or switched on. This issue has also been mentioned elsewhere including on the Phase One forum.
Have opened a support ticket on this issue. While there's been no resolution to this issue thus far, its been suggested that this might be a display card/software issue. While not an effective solution, down-grading to version 7.1.712 bypasses this issue, meaning to say, everything works as intended.
Hope this helps - Rogan