Hello. Having that type of issue could be caused by many different issues. Not bugs, but setup issues usually. First, make sure you update to the new 2.7.2 package. Also be sure you are using the very latest version of our plugins and module. Also check the following (just some guesses as there is no way to give a definite answer blindly here in the forum):
- make sure you are running PHP 5.2 or later
- make sure any 3rd party SEF components are set to "Skip" DT Register
- make sure you do NOT have our JomSocial plugins installed unless you actually have the JomSocial component installed
If you can't get things sorted after updating everything, submit a ticket.