I have several conflicting reports of people both getting access to FamilySearch.org's Family Tree and not getting access. In the access category are definitely people who have used New.FamilySearch.org sometime in the past and updated their LDS Account to a not-so-new password and login. If you can access New.FamilySearch.org and LDS.org, you should have little or no trouble opening Family Tree when you sign in to FamilySearch.org or use the link from New.FamilySearch.org.
If you have never registered with FamilySearch before to access New.FamilySearch.org, evidently that may keep you from registering right now. This limitation will be removed very shortly apparently when they are sure the program can take the number of users.
This may be somewhat technical, but the conclusion is if you can get onto the program you can, if you can't get onto the program, maybe you can't. I will see if I can get any more updates from readers who either are successful or not in getting into the program.
If you are reading this and hearing about FamilySearch Family Tree for the first time. I realize all this can be baffling. Please take the opportunity to go to FamilySearch.org and read about the new program in the Help menu. See the link to Help in the upper right-hand corner of the startup page.