Hi All!
To add to Alberts suggestion, since /System/Library/Keychains will likely not allow you to copy the SystemCACertificates.keychain inside, try to download to the desktop. Then in step 3, instead of browsing to System>>Library>>Keychains to locate the file, browse to the file on the desktop instead.
Again, the steps are:
1. Open Keychain
2. Click File>>Add Keychain
3. Browse to Desktop and select SystemCACertificates.keychain and click 'Add'
Please let us know if this solves the issue.
Thank you!
Have a great day!
Ryan V.