School computers don't always "talk" to your work from your home computers. The following are a few options when you're having trouble opening an attachment from your email:
1. Save the file instead of downloading/opening. Then go to the program you'd like to use and open the file from inside the program (use the open icon on the menu bar).
2. Save the file. Open your Google account, go to your Google files and upload the file. Open the file from inside your Google account. The file might not look exactly the same as it did at home, but it could be better than having nothing!