I got this error. Is that possible? Really need so much memory?
Depends on how many users you have and if any fatal errors occurred. The internal users trigger executes for every user row. So if you've say 200,000 users for example that's a lot to process. If a fatal error occurred then it'd explain excessive memory usage though. Ensure debug mode and maximum error reporting is enabled when testing so the full error and callstack is exposed.
The confirmation link seems not working: index.php?option=com_comprofiler&task=confirm&confirmcode=[cbactivation]
That exact link isn't going to work. Substitutions need to take place to replace [cbactivation] with the actual activation code in _comprofiler.