KM Content - Logon popup

Hi,

I have created an iView and used that iView to store the KM content like folder/sub folders and files. Now the problem is when we upload the files in the folders and then try to open the files as a normal user. All the microsoft files like word, excel, powerpoint, when we open them, we get a pop up to give our network user name/password and it's coming every time which is not acceptable. Other files like PDF are ok, we don't get any popups in this case. Only Microsft word, excel, powerpoint files generates a popup, so even if we cancel the pop up with out entering the credentials - the document will be opened.

Any idea what's wrong...any property settings on Iview level or any other thing....

Thanks,