It's Stuart here from the BackupAssist team, thanks for your post.
Did you re-format the drive at all just to refresh the drive (I have seen this happen previously).
If you have done this and it's still failing at 4Gb, would you be able to provide some diagnostic information as
this gives us a lot of information which we can use to help resolve your issue.
To send us diagnostic information please follow these steps:
1) Go to Contact Support (from the bottom-left corner of the console) -> Contact Support
2) Fill out the form and ensure that the Submit system diagnostics checkbox at the bottom is checked.
If you have anything to add Pam, please either reply to this post or send us an e-mail directly at email@example.com