To aid: Try running the /cleanfreebusy command switch: Clears and regenerates the free/busy information on the Exchange server. This switch affects Outlook and OWA data, and can only be used when connected to Exchange.

To run Outlook with a command line switch, use the following steps:

Windows XP:

• Click Start.
• Click Run.
• Enter the following in the Run dialog box (with quotations):
  "c:\program files\microsoft office\office11\Outlook.exe" /Commandswitch
• Click OK.

Windows Vista/7:

• Click Start.
• Click All Programs.
• Click Accessories.
• Click Run.
• Enter the following in the Run dialog box (with quotations):
  "c:\program files\microsoft office\office11\Outlook.exe" /Commandswitch
  
  Note: For 64-bit Operating Systems, you will enter the following (with quotations):
  "c:\program files (x86)\microsoft office\office11\Outlook.exe" /Commandswitch
• Click OK.

hope this helps: