Hi, We are seeing the following warning event being generated on our Exchange Server 2003 (SP2) servers across 3 sites Source : EXCDO Event ID: 8241 An existing appointment with the subject "" in mailbox user@domain.com was modified. The start time, or both the duration and end time of the existing appointment were missing. I have been searching around Technet, Premier Support and general Google searches for the last couple of days but I have been unable to find any relevant information. If anyone has any ideas on what is causing this error and more importantly, how to fix it, it would be greatly appreciated.

Hi Is here any type of logic when it happens? What about the backup?Jonas Andersson MCTS: Microsoft Exchange Server 2007/2010 | MCITP: EMA 2007/2010 | MCSE/MCSA Blog: http://www.testlabs.se/blog

Hi, Clarify: Please help me to clarify the following information: 1. Is there any other error in your event log? 2. Is the mailbox the same in all the Error 8421? Troubleshooting: 1. Ask the calendar user to save the calendar items to a .pst file. You can do this (in Outlook) by this way: File->Import and Export, select Export to a file->Personal Folder Files, select the Calendar folder and choose the default options 2. Use MFCMapi to rebuild the user’s calendar. a. Download MFCMapi, you can download MFCMapi from this link: http://mfcmapi.codeplex.com/ b. Before running MFCMapi, ensure the Outlook profile is configured to run in Online Mode. If not, please change the profile by this way: Control Panel-> Mail->E-mail Accounts->choose the account->change->uncheck “use cached Exchange mode”->next->finish 3. Logon to the mailbox using MFCMapi: Open MFCMapi->Click OK on the MFC Editor window->Session Menu->Click logon and Display store Tale->Select the using profile->Double click on Mailbox -<User Name> 1). Drill down to Root Container -> Top of Information Store -> Calendar->Right-click Calendar-> select Open Contents table. 2). Delete All the items from within the folder, and close the Calendar dialog box. 3). Remove the Calendar folder by right-clicking Calendar under Top of Information Store and Selecting Delete Folder. 4). Click Start -> Run, and type Outlook /Resetfolders and click OK (in Windows, not MFCMapi). 4. Use import option to import calendar items back from the pst file. Note: All these steps are tested in Outlook 2007, in Outlook 2010 and Outlook 2003, there may some different on the steps(how to import and export .pst file). If the problem persists, please feel free to let me know. Thanks, Evan

Hi Evan, Thanks for the reply. This error is occurring for a couple of hundred different mailboxes and there are no other errors in the event log around the time of these appearing. The errors are still occurring across all 5 Exchange 2003 servers. Thanks again for your reply.