RDS License server reporting no remaining licenses (event ID 21 TerminalServices-Licensing)

Problem:

I am seeing the below event in our RDS licence server every 15 mins. 

Log Name:      System
Source:        Microsoft-Windows-TerminalServices-Licensing
Date:          11/11/2014 16:27:21
Event ID:      21
Task Category: None
Level:         Warning
Keywords:      Classic
User:          N/A
Computer:     SERVER.domain.local
Description:
The Remote Desktop license server "SERVER1" does not have any remaining permanent licenses of the type "Windows Server 2008 or Windows Server 2008 R2 : Per Device CAL (TS or RDS)". As a result, the Remote Desktop license server cannot issue licenses of the type "Windows Server 2008 or Windows Server 2008 R2 : Per Device CAL (TS or RDS)" to the Remote Desktop Session Host or Remote Desktop Virtualization Host server "IP of another host server". To resolve this problem, verify that the Remote Desktop licensing mode configured on the RDSH or RDVH server matches the type of licenses installed on the Remote Desktop license server. If required, purchase and install additional licenses as needed for this Remote Desktop license server.
Event Xml:
<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
  <System>
    <Provider Name="Microsoft-Windows-TerminalServices-Licensing" Guid="{4D99F017-0EB1-4B52-8419-14AEBD13D770}" EventSourceName="TermServLicensing" />
    <EventID Qualifiers="0">21</EventID>
    <Version>0</Version>
    <Level>3</Level>
    <Task>0</Task>
    <Opcode>0</Opcode>
    <Keywords>0x80000000000000</Keywords>
    <TimeCreated SystemTime="2014-11-11T16:27:21.000000000Z" />
    <EventRecordID>20596</EventRecordID>
    <Correlation />
    <Execution ProcessID="0" ThreadID="0" />
    <Channel>System</Channel>
    <Computer>SERVER1</Computer>
    <Security />
  </System>
  <UserData>
    <EventXML xmlns:auto-ns3="http://schemas.microsoft.com/win/2004/08/events" xmlns="Event_NS">
      <param1>SERVER1</param1>
      <param2>Windows Server 2008 or Windows Server 2008 R2 : Per Device CAL (TS or RDS)</param2>
      <param3>IP</param3>
    </EventXML>
  </UserData>
</Event>

My checks:

• There are no issues identified in the license diagnosis on any of the hosts pointing to this RDS license server. 
• All hosts are set to "per device". 
• Activation status is "activated"
• Discovery scope is "domain"
• Configuration is "ok"
• I've deactivated and reactivated the licence server
• repeated the install of the licences and rebuilt the potentially corrupt database. 

Any ideas from anyone? 

Craig Brand