Recently upgraded some machines from Windows XP SP3 to Windows 7 SP1 (fresh install). Couple of users started experiencing serious issues with their Outlook 2010. Soon after starting Outlook would hang and then crash. Outlook.exe process, however, would stay in the task manager and nothing would kill it. New Outlook instance would refuse to start as well. Following methods were tried to kill the hung outlook.exe (we are logon on as Administrator):

• Windows Task Manager
• Sysinternals Process Explorer
• taskkill
• taskkill via psexec under Local System account
• pskill

taskkill was giving error:
ERROR: The process with PID <xxx> could not be terminated.
Reason: There is no running instance of the task.

All other methods would give Access Denied error.

Even shutdown would not stop the process! Computer would simply hang while Logging off… The only option was to hold down the power button. 

The problem in this particular case was caused by Outlook archives (.pst files) stored on network shares. Moving .pst archives to a local drive fixed the issue on the affected machines.

Microsoft doesn’t recommend storing .pst files on the network, but it was quite difficult to explain to users why they should stop doing this when it worked perfectly well in Windows XP and they have been doing this for years…

For me, the most worrying issue was Windows 7 inability to kill a hung process. I thought days when crashed applications were taking down Windows were long gone, but it seems that I was wrong…