Encountered error when exporting images using Lightroom

Hi,
I got this error message (see screenshot below) when I exported images from a catalog using Lightroom. The catalog contains hundreds of images and it would be difficult to look for corrupted images which one site recommended doing.
Anyway, experts here might help me find an easier way to resolve the problem.
Please help!

Error:
LR
Unable to Export:
An internal error has occurred: ?:0: attempt to index field ‘rootFile’ (a nil value)
