Some times, you will view an error message as displayed in the figure below. The error occurs when you attempt to upload an ASP.NET script which make use of System.Net.Http.Formatting assembly but you have not uploaded it inside the relevant folder.
In order to fix the above error, you need to upload System.Net.Http.Formatting.dll file inside BIN directory through FTP. You can locate the DLL file inside the original ASP.NET script package.
Reload the web page and verify whether your site is working or not. If the applications throws any new error, you need to fix them by going through the error message or by estalishing contact with the developer.
Note: You should always create a copy of any ASP.NET script before making changes. This will be handy in case if you mess up any settings.