Wilfred,

 

You need modify the NTFS permission of that folder , to allow IIS/ASP.NET account write it.

 

Another solution is specify the account who can access that folder (not recommand)

 

 <add key="CuteWebUI.AjaxUploader.WindowsUsername" value="username" />
 <add key="CuteWebUI.AjaxUploader.WindowsPassword" value="password" />

 

Regards,
Terry