If you are unable to boot a Symantec Endpoint Encrypted client computer and need to take a backup of the data saved on the encrypted drive, you can try recover the data by using a WinPE disk.
This applies to Endpoint Encryption 11.0.0 version onwards.
There are two methods that can be tried to recover user data from an encrypted drive. Both ways require you to boot the encrypted client computer with a WinPE disk.
Authenticate the Disc with a command to access and copy Files to External USB Drive.
Decrypt the hard drive using eedRecoveryGui and copy Files to External USB drive.