Sometimes you create a new user via Active Directory Users and Services instead of creating it through the SBS user creation wizard.
Now this is how to make it appear into you SBS user console.

Step 1

Open ADSI Edit

Step 2

Browse for the OU where your user is created

Step 3

Once you've found the user you are looking for, right-click on it, click on properties

Step 4

Look for an attribute called "msSBSCreationState"

Step 5

Change the value for this attribute to "Created"

Step 6

Refresh you SBS user console, the user now appears.

NOTE : The user appears in the SBS Console with no "user role" assigned. Select your user and click on "change user roles for user accounts" in order to reassign a role.