I searched this problem but the answer look out-dated. The org I'm working on has a public site (named 'Aste'). I am sure I could go to the debug logs and set a tracked user either with 'Aste' or 'Aste Profile Guest User'. Since a couple of days this is no longer working, no error is given in the form where I put the name of the tracked user but when I see the debug-logs page nothing is there and nothing is logged.
Did something change about Sites debug-logs lately? Thanks very much for your assistance