SSL Technical FAQs
This file is invalid for use as the following: Security Certificate
This is not an error, it simply means you cannot open the file.
To view the certificates in the file, change the file extension from .cer to .p7b
Now, when you open the file and open the branch on the left of the window you will see 'Certificates'.
By clicking on 'Certificates' you will see all the certificates contained in the single .cer format file.