Different keyboard layouts can have different mappings between characters, potentially causing problems when you enter your passphrase to authenticate. Select the keyboard layout that most closely maps to the keyboard you are using, then make sure to use that same layout each time you authenticate.
Be sure that you are using a keyboard with one of the supported languages. On Microsoft Windows systems, the Drive Encryption functionality of Symantec Endpoint Encryption 11.x supports the following keyboard layouts for preboot authentication: