Hey there, Nishanthallam!
Does this disconnecting happen often or was it a one-time thing? I'd suggest to try the external with a different USB cable if the unmounting happens regularly.
I'd also suggest to take a look at a couple of links that might help you with the BitLocker protection:
https://technet.microsoft.com/en-us/library/ee523219.aspx
http://answers.microsoft.com/en-us/windows/forum/windows_7-security/cant-access-to-drive-after-typing-bitlocker/443c8c10-8b83-4754-849f-fedb90ab1231
Hope this helps you! Good luck!
SuperSoph_WD