Looking at the list of error messages it appears that error code E means that it's external. Possibly an issue on your friend's side.
That being said it could be something with your NAT. I know I had issues with my NAT and party chat when I first setup my PS4. What does tthe network connection test say your NAT type is on your PS4?
NAT 2 is good. That's what it should be. Is this also when access your friends list? That seems to be the issue with OP. Does this happen when you're attempting to enter party chats? When does the issue actually occur?
I'm still going to assume it's a NAT issue. Have you opened ports on your router?
I had issues with my party chat before i opened ports on my router.
Look over this article. See if that helps you.