Virtual directories in IIS

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IIS

I access completely to a shared drive in windows server 2008.
Then I created a web page using ASP.NET which lets users upload pictures and films to the server. But it was needed to transfer the uploaded files to that very drive.
To meet the end, I created a Virtual Directories in IIS and I Chose that physical address in the shared drive path; also, I set a password to access that drive.
However, there is a problem to be tackled. That is, I can display the files uploaded in the drive on the web, but I cannot upload any thing from the web to the drive. In fact, I just read and cannot to write or delete (Merely via uploading files of the web).
How can I set writting access in IIS in a shared drive?

What I have tried:

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