If the default profile in the “Mail” Control Applet is unclear, you can always check it by looking in the registry at the “Default Profile” value in “HKEY_CURRENT_USER\Software\Microsoft\Windows NT\Current Version\Windows Messaging Subsystem\Profiles”.
Microsoft KB article 951644 has more information on how to resolve this situation.
#3) Check if the Microsoft Exchange Administrator tool(s) are installed the client machine.
The resolution is to run (in C:\WINDOWS\system32\fixmapi.exe).
This resolution has worked on 32-bit XP machines with SP2 and Sp3.
#4) Make sure that Office 2007 and Office Communicator are up-to-date (i.e. Specifically make sure the hotfix described in KB 936864 is installed.
March 2013 Update: a good Microsoft resource I recently discovered: Resolve Exchange Free/Busy and Communicator Presence Issues.
Further to my previous posting on Office Communicator 2007 and Outlook 2007 Integration Errors, after recently trouble-shooting this problem, I have provided a check-list of all the situations I am aware of that can cause this error, and what to do about it.
Communicator integrates with Outlook (on the client machine) to retrieve availability data for Enhanced Presence (e.g. In Office Communicator 2007 R2 any Outlook integration errors appear as a red exclamation on the Communicator icon in the Windows task tray, and as a missed notification in the Communicator GUI (which you can click to get more details about the error).#1) Has Outlook been successfully configured on the client and connected to Exchange at least once?I have read if Outlook is not started, Communicator will display an integration error.This is not true (at least in Office Communicator 2007 R2).The integration works fine if Outlook is not running, but Outlook must have been successfully configured (and run once) however.#2) Make sure that the default Outlook profile, or the Outlook profile that was last used (if set to prompt), contains an SMTP Email Address that matches the users’ primary SIP address.