E-mail policy reapplied every 1-2 minutes - Error 31506 Microsoft Forefront TMG Control

I'm running Exchange 2010 with only the Edge Transport-role on a Windows 2008 R2-server with Forefront TMG and Forefront Protection Manager for Exchange. I have an error message in application log every 1-2 minutes:

Log Name:      Application
Source:        Microsoft Forefront TMG Control
Date:          25.12.2009 21:05:28
Event ID:      31506
Task Category: None
Level:         Error
Keywords:      Classic
User:          N/A
Computer:      TMG.ad.artax.cz
Description:
Forefront TMG detected changes in Microsoft Exchange Server or Microsoft Forefront Protection configuration, and reapplied the e-mail policy configuration on server 'TMG'.
Event Xml:
<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
  <System>
    <Provider Name="Microsoft Forefront TMG Control" />
    <EventID Qualifiers="32768">31506</EventID>
    <Level>2</Level>
    <Task>0</Task>
    <Keywords>0x80000000000000</Keywords>
    <TimeCreated SystemTime="2009-12-25T20:05:28.000000000Z" />
    <EventRecordID>8101</EventRecordID>
    <Channel>Application</Channel>
    <Computer>TMG.ad.artax.cz</Computer>
    <Security />
  </System>
  <EventData>
    <Data>TMG</Data>
  </EventData>
</Event>

I am not changing anything. No error on Exchange server (Hub Transport) and everything seems to be working.

Could you help, please?

Best regards

Martin