I have same issue.
I bought photoshop and premiere elements 15 in Jun. I am able to install and validate and using photoshop elements 15 since then.
Now I decide to start using PRE 15. So I install it, but it does not allow me to activiate it, not able to sign in due to not able to connect to internet. Which is definitely not true.
The photoshop E 15 is still running. I can see the Help that I am still signing in, with "Sind Out" option.
I try to sign out from PE15, but it fails as well, saying the same thing "Unable to connect to internet".
So now I have Photoshop Element 15 signed in, not able to sign out, PRE 15 not able to validate and sign in.
WHAT'S WRONG ?!
Did you follow Bill's advice, above?