Can't open Office 2007 file from link

i have a web app that links to documents stored on a server which was working fine until users started uploading 2007 files with the .docx extension for example.
if i use the UNC path it works fine but i dont want to use that method.  Is there anything special that has to be done to open the 2007 files from a .net web app?

 

thanks
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