Hello there, this problem is not to ask for tricks to delete files, such as change owner and grant permision, etc. Basically, we installed an application, but somehow when we install the new version of this application, it tells us we do not have the access privilege to the directory we installed the application before, somewhere under program files folder. By the way, I am the administrator user and I can't open or even delete this directory. However, after I reboot Windows, everything was Ok. I am asking why this happen, why the reboot matters? Please help :)

"...after I reboot Windows, everything was Ok." So I take it the problem was fixed by a reboot then? Some config settings require a reboot, especially when those involve changes to the registry & other config settings.

I agree with cschaar, there are many instances where files and settings are "in use" by windows.John Wiley

I've been having the same problem. Posted my own topic a week or so ago, http://social.technet.microsoft.com/Forums/en/w7itprosecurity/thread/a173060a-4a4c-4825-920b-8e17077ad6e6 I've narrowed it down to windows installer (msiexec.exe) remaining open after an installation indefinitely. Once you close that process it takes about 10 minutes to restore permissions to an install directory. Take a look at the posts from Kerry Brown, The guy's an idiot. Doesn't even know the difference between a file in use and a permission denied error. We need a patch for this bug. It's starting to impair my ability to do anything in windows. I've already started converting all my systems over to linux. Basically everything can be run from wine anyways. I already plan on not purchasing another Microsoft product ever again. (they're better than Mac, but they're not that far ahead) And for the reference of any admins/mods I know what i'm talking about. I've done my A+, Network+, and Microsoft 680 TS: Configuring Windows 7. I know a great deal about permissions, enough to deal with anything this buggy software can throw at me. This goes way beyond bugs. This is a core vulnerability and should be of utmost importance.