When the 6th user attempts to log on to the domain, they are denied access. The Application event log contains:
Event 201: No license was available for user <user_name> using product SMBServer 4.0.
If someone logs off, the 6th user can log on.
To resolve this problem:
1. Check the number of installed licenses:
Start / Manage Server / About Microsoft BackOffice Small Business Server
2. Use Regedt32 to navigate to:
Edit or Add Value name ConcurrentLimit, a type REG_DWORD entry, and set the data value to the number of licenses from step 1, using the Decimal Radix.
3. Use Control Panel / Services to Stop and Start the License Logging Service.