There are different ways to work around this issue:
Solution #1 ( Preferred )
The simplest and most secure method to get around this issue is to simply click the Enable Editing button, on a per-document basis, when you open an Excel (or other Microsoft office) file that has been downloaded.
Solution #2 ( Not Preferred )
Alternatively, you can choose to disable the Protected View feature within Excel so that you no longer recieve the warning upon opening any Excel file that has been downloaded.
-> go to File
-> Trust Center
-> Trust Center Settings
- > Protected View, and then
->uncheck Enabled Protected View for files originating from the Internet.
There is also, in Trust Center Settings, a Macro Setting that you can use to Enable All Macros by default
Note:Be aware that enabling this feature allows potentially dangerous code to run.If either of these Trust Center settings are changed, you need to be very careful about the Excel files which are opened