I have worked with MSO365 support to migrate my domain to 365 and I downloaded the updates for my Office 2007.  Everything seems to have worked well except  that when I start Outlook in the morning I get a message that it can not find the file Extend.dat.  On the advice of support folks I created new Profiles for my email service but this has not resolved the issue.  I even deleted all of my old profiles thinking maybe it was one of the old profiles that ws causing the problem.  I am hoping I can still get into the the old archive files if I need to see old emails.

But the bottom line is I would like to fix what ever is wrong with Outlook so it does not show the error message that it can not find Extend.dat.  Does someone have a fix for this problem?

Hi geocoy,

This behavior can be caused if the Extend.dat file is corrupted. I suggest renaming the file  Extend.dat to troubleshoot this issue. The detailed steps are provided as below:

1. Close Outlook 2007.
2. Using Windows Explorer, go to: %USERPROFILE%\Local Settings\Application Data\Microsoft\Outlook
3. In the Outlook folder, rename the extend.dat file to OLD_Extend.
4. Restart Outlook and check whether issue persists or not.

Thanks,
Mindy Pan

Hi geocoy,

Thank you for sharing the solution with us. I’m glad to hear that the issue has been resolved. I believe other people who encounter similar problems will benefit from this information.

I would like to share the following websites with you. You may find some useful information about Office 365.

For Office 365 Small Businesses:
http://onlinehelp.microsoft.com/en-us/office365-smallbusinesses/

For Office 365 Enterprises:
http://onlinehelp.microsoft.com/en-us/office365-enterprises/

Thanks,
Mindy Pan

You'll be happy to know I found the extend.dat file myself.  In Outlook If you go to the Tools menu/ options/Mail Setup/Email Accounts/Data files/Choose a mail box -- and then choose Open Folder it takes you to the directory we were looking for.  I changed the name of the extend.dat to Oldextend.dat and restarted the program.  It created a new extend.dat file.  The old one must have be corrupt.

Error Message resolved.

I found this by luck when I was trying to get my new email profile to use the default "Contacts" list.  I think we are done here, but I have to tell you this is way more than what I wanted to know about Outlook.  It is in a world of its own.

This is what I was telling you, my Windows Explorer is not allowing me to see this path.  There must be a setting that is wrong that is blocking me from seeing the path I need to see.  Can you help me with these settings so I can see the correct path.

Hi geocoy,

Open Windows Explorer, and locate the C:\Users\ <user> \Local Settings\Application Data\Microsoft\Outlook folder, and then check if the extend.dat file is shown in the Outlook folder. If so, rename the file to OLD_Extend.

Please note: Remember to replace '<user>' with your Windows user account.

Thanks,
Mindy Pan

I have tried to find this file and I can not find it.  I am having a little trouble deciphering your parameters, I can not find the path you are referring to  in "%USERPROFILE%\Local Settings\Application Data\Microsoft\Outlook"

My root files on my C:\drive from a windows explorer view look like this, so I am not sure where to go from this view.  I have to tell you I am not happy with the way this version of Windows Explorer works, it often combines files from different directories into what looks like a single directory making it difficult to find the location of particular file.  Let me know what you want me to do.