It sounds like you are talking about WD2go. If that is correct, then this will be related.
First you should check to see if there is a password on your MBL. Go to the UI http://mybooklive or whatever you have it named.
If it prompts you for a password, then you know there is one already set.
If you know it, then log it.
If you don't know it, then hold down the reset button for 4 seconds. That will reset the password and network settings, but will not affect your data.
Once you are logged in you can change the "Admin" password by either clicking "Secure your device" in the upper right corner, or by going to "Users" and clicking on the Admin user. The right pane will give you an option to change the password.
If this does not help you log into WD2go, then just delete the account and create it again. Perahps something glitched.
Actually, you might just try removing the drive from WD2go, and the account from UI >> Mobile Access >> Remote Access.
Then recreate it. That might solve your problem up front and simply.