Outlook 2007 crashes or you cannot access OOF settings after you install a package that contains the .NET Framework 3.5 with SP1 and the .NET Framework 2.0 with SP2 on an Exchange 2007 Client Access server or on an Exchange 2010 Client Access server

You may experience one or more of the following symptoms after you install a package that contains the Microsoft .NET Framework 3.5 with Service Pack 1 (SP1) and the .NET Framework 2.0 with Service Pack 2 (SP2) on a Microsoft Exchange 2007 Client Access server or on a Microsoft Exchange 2010 Client Access server:

• When you click Out of Office Assistant on the Tools menu in Microsoft Office Outlook 2007, you receive the following error message:
  Your Out of Office settings cannot be displayed, because the server is currently unavailable. Try again later.
• Outlook 2007 crashes when you try to view a user's free/busy information.
• When you open the Scheduling Assistant tab in a meeting request form in Outlook 2007, you cannot view free/busy information. Instead, you see hash marks in the free/busy grid.
• When you run the Test-OutlookWebServices cmdlet in the Exchange Management Shell on the Client Access server, you receive the following error message:
  Object reference not set to an instance of an object.
• When you examine the information in the OOF log on the Outlook client you see the following entries:
  Response error code: 00000000
  HTTP status code: 0

Note Currently, there is no separate package for the .NET Framework 2.0 with SP2. The .NET Framework 2.0 with SP2 is included in the .NET Framework 3.5 SP1 package.

This issue is caused by a problem in the package. This problem only occurs when the package that contains the .NET Framework 3.5 with SP1 and the .NET Framework 2.0 with SP2 is installed on an Exchange Client Access server.

To resolve this problem, install the hotfix that is described in the following Microsoft Knowledge Base article on the Exchange Client Access server:

Warning Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. These problems might require that you reinstall the operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk.

To work around this issue, follow these steps:

• Use Outlook Web Access to configure Out of Office (OOF) messages.
• If you have public folders in the Exchange 2007 environment or in the Exchange 2010 environment, force Outlook to use public folder free/busy information instead of the Availability Service. To do this, follow these steps to add registry data to the Outlook 2007 clients:
  1. Click Start, click Run, type regedit, and then click OK.
  2. Locate and then click the following registry subkey:
     HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\Options\Calendar
  3. On the Edit menu, point to New, and then click DWORD Value.
  4. Type UseLegacyFB, and then press ENTER.
  5. Right-click UseLegacyFB, and then click Modify.
  6. In the Value data box, type 1, and then click OK.
  7. Exit Registry Editor.