Welcome to the community, Priyanka_1!
What is your Mac OS X version?
I'd recommend you to check how the external drive appears on a Windows PC first and see if you can access it from there. If you can, I'd recommend you to try disabling/removing the encryption until you've transferred the files successfully to your MacBook.
If you don't have access to a PC, you can try using Disk Utility in Mac OS X and try to 'Repair Disk'. The utility will help you scan the drives for any kind of defects.
Keep me posted.
SuperSoph_WD