The problem seems to be the fact that you placed the files in the Desktop of the Administrator, this means that no one else but Administrator can read the files in there including IIS. You need to grant read permissions for the worker process to be able to read the file. You can do this by running the following command line:
icacls C:\Users\Administrator\Desktop\WebGUIApplication1\ /grant "BUILTIN\IIS_IUSRS":(OI)(CI)(RX)
If you want to be even more explicit you can only allow the particular AppPool that will be running the requests to read it by doing (assuming its running in the DefaultAppPool):
icacls C:\Users\Administrator\Desktop\WebGUIApplication1\ /grant "IIS AppPool\DefaultAppPool":(OI)(CI)(RX)