I am running C# ASP.NET 4.5 web application on Windows 7 64-bit using IIS 7.5. The application pool it uses has the name \'ASP.NET v4.0\' and its identity is ApplicationPool
I too encountered the same scenario and found out two solutions after googling for several times. Hope this helps.
Way 01:
Before trying to open the file in Excel, find it in Windows' File Explorer. Right-click the file and select Properties. At the bottom of the General tab, click the Unblock button. Once you unblock a file, Windows should remember and Excel should not ask you again. This option is available for some file types, but not others. If you don't have an Unblock button, use Way 2.
Way 02:
This option is better if you usually store your downloaded Excel files in one folder. In Excel, click File » Options » Trust Center » Trust Center Settings » Trusted Locations. Click Add new location. Browse to the folder where you store your Excel files, select Subfolders of this location are also trusted, and click OK.