Could be a defective connection cable, a defective card reader, a damaged USB port or connection on the computer itself, a defective card or one with bent pins, etc.
Only trial and error testing will tell.
Try a different reader, different cables, even a different computer to track down the culprit.
Incidentally, you don't "import" image files "into" Bridge. You're simply copying them over to your hard disk and then viewing them there with Bridge.
So try just drag-copying them yo your hard disk in the Mac Finder or Windows Explorer.