I'm not sure what is causing the problem, but we're seeing a rash of complaints with the following error:
"Cannot start Microsoft Office Outlook. Unable to open the Outlook window"
The users run Office Diagnostics in an attempt to fix it on their own but it finds no errors.
To fix this you need to close Outlook and reopen it using the /resetnavpane switch or find and delete <profile_name>.xml and restart Outlook. Outlook will recreate a new file with the default navigation pane folders. You will lose any customizations on the navigation pane, such as folders on the Favorites folder list
This problem may occur on Windows XP if you are running Outlook in Compatibility mode. Compatibility mode is NOT needed with any version of Outlook on any versions of Windows.
How to use the /resetnavpane switch
Close Outlook. At the Start search field on Vista or Windows7 Start menu or in the Start menu, Run command (Windows key + R), type or paste
outlook.exe /resetnavpane
Then press Enter (or OK button) to restart Outlook.
Note: Make sure there is a space between the words.

Video Tutorial
Delete the Navigation pane configuration file
If you are having problems using the switch, you can find and delete the XML file that holds the navigation pane settings. In the Start search or Run fields or in Windows Explorer's address bar, paste the following and press Enter:
%appdata%\Microsoft\Outlook
This will open Windows Explorer to the folder where many of Outlook configuration files are kept. Find and delete the file named for your profile with the extension XML. Note that we highly recommend using the switch instead of deleting the file directly.
More Information
From Outlook-tips.net:
Microsoft KB articles
See Error with the To-Do Bar's Task list if the error is "The operation failed. An object could not be found."
Articles that may interest you:
Last reviewed on Feb 25, 2012


I am using Windows 7 Professional with Outlook 2007. I am receiving the same error. I tried running the /resetnavpane command line and starting in safe mode. Still having the same issue.
Any suggestions?
I tried both; outlook.exe /resetnavpane and %appdata%\Microsoft\Outlook .
Everytime I delete the old xml files and pst from the Remote and local folders in outlook, they come back when I attempt to open outlook again. So I get the same error and cannot open outlook. I have uninstalled numerous times and reinstalled it with the same results.
Does anyone have any other ideas?
They are supposed to come back, but the error shouldn’t. Is Outlook configured to run in compatibility mode? Did you try a new profile?
I can’t open outlook either….and neither of these solutions worked…mine says errors have been detected in the outlook.pst files…..but I can’t find them….or the scanpst.exe file to diagnose and repair……HELP!!???
See How to use Scanpst for step-by-step instructions to find scanpst and use it. If, by chance, you have Office 2010 Home and Business click to run you won’t have scanpst.
tried all above, the problems started after a SW update from Mirosoft in December 2011, same exchange works on my laptop fine, but on the desktop it is only working when i use the outlook /safe switch..
Same as Thomas McKean above –
Message panel reads: Cannot start Microsoft Office Outlook. Cannot open the Outlook window. The set of folders cannot be opened. The file C:\Users\…\Outlook.pst is in use and cannot be accessed. (etc.)
Followed both of above, no effect. Logout/login does not affect this.
This problem only goes away by rebooting, which now takes about 15 minutes. It’s happening daily and is a real nuisance.
There appears to be a file lock on the PST file, left over some some Outlook bug. Not sure how to release it, except through a reboot.
Outlook 2007. Vista OS.
outlook 2010 bliver ved med at spøre efter produtnøgle ,
When Outlook keeps asking for the product code, close it and restart using Run as Administrator – enter the code. The next time you restart it should be fine.
I am unable to open Home and Business Outlook 2010 in Win7. Version is 14.06029.1000. It worked fine earlier today. I was entering contacts. The file size is 265 KB. I am unable to run the nav file, but did find the .pst file and restored it. Still no luck. The application icon does not open it. Safe mode does not work. I do not feel good enought to change any other programming.I am unable to access my mailboxes from this computer.
I checked the properties of the Outlook pst file and noticed that the attributes on this file show an Al and not A like the other office folder shortcut. The desktop shortcut is an A.
Help, please.
Joy
265KB means the file is empty.
Go to My Documents \ Outlook Files – how many pst files are there? What is the last modified date and large are they?
Paste %localappdata%\microsoft\outlook in the address bar of windows explorer – check the file date and size of the pst files here.
Go to control panel, search for mail. Edit the profile by adding the largest pst file to your profile and removing the 256kb pst. Will outlook open? If so, do you have your recent email?
After uninstalling the updates of today’s date (ist update), I was able to open Outlook in safe mode. There were three to remove. I did that in the order last in first out. I now appear to ba able to open it and added a contact, as I had tried restoring to the previous day, without success. As a result I had lost the entries of today. Hopefully, it will work the next time.
There was only the one pst file and I restored that to the previous day, without successfully curing the problem, which appears to have come from one of the updates to Outlook.
Yea, it opened normally. Now I will turn off updates, when I fugure out how to do that. Thanks for your help.
Joy
If you know the update that is the problem, go to windows update and hide it. This will allow other updates to install automatically. Also, sometimes the reinstall works, so its not always necessary to hide them. But, in most cases the update is not critical so hiding them is fine.
“Outlook.exe /resetnavpane” worked for me. Thanks.
While I’m making a mail setup on outlook,I made a check on manually after making it I can’t open the outlook