Welps, it seems the PSN client is ID tied.

I opened up the freshly downloaded and installed client I got from redeeming my EU PSN code on my EU PSN ID. I got the same error, and it asking me to re-enter my code (which doesn't work on my US PSN ID.)

So I switched over to my EU PSN ID and launched the client, it worked fine. I'm going through the setup to see if I can bind the info to my SE Service Account...

HOWEVER, if this works, for PS3 users I get the feeling they'd have to use their EU PSN IDs to launch the client. Going to test it now...