When you setup the backup2workstation via the server manager, you must include permissions. This is the admin login and password of your SME box. This will grant permissions to execute the backup job.
Heres a checklist:
Create shared folder on Wkstn eg. backup_sme
In server manager create backup
Fill in details - be sure to check the name of your wkstn
Add admin and password
The successful job should look like the following
# ----------------------------------------------------------------
# Backup report for Win_backup, job number 996383:
# ----------------------------------------------------------------
The backup is now complete.
See /var/log/backup2ws/996383.log for complete details.
I use SME 6.0 and 6.01
Give it a try and see how you go
Good Luck
Rob