Please Halt all communication about the beta in a public forum, please follow the link below to get answers to your issues.
"Group Not Found" issue. This can take up to 3 business days(Mon-Fri.).
Not everyone has access yet, please post at that link with beta questions, when it comes, up.http://forums.xbox.com/xbox_forums/beta-2013/default.aspx
Note: You are required to agree to a non-disclosure agreement (NDA) for confidentiality reasons. Any participant who violates the NDA will be removed from the beta, be barred from future Xbox betas, and not have access to Xbox LIVE until the end of the beta program period. Your NDA does apply to posting in the public forums. Make sure not to post any feedback, comments, or suggestions about the beta there!
If you still cant access the forum, please wait till the rest of the day, as people are still being allowed access.