Access to the path is denied

Seems like a simple problem... one I've dealt with many times before and been able to solve. I'm developing on Windows 7, VS 2010, .NET 4.0.
Code:
Dim webClient As System.Net.WebClient = New Net.WebClient
webClient.DownloadFile("....IMGP9237.jpg", Server.MapPath("~/free_images")
Error:
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Access to the path 'C:\....\free_images' is denied. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.UnauthorizedAccessException: Access to the path 'C:\Sites\free-wolf-photos\free_images' is denied.
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