Cannot login into ADMIN areea ....

It asks for authentication all the time, and goes on only after the 3rd try but then again you have to authenticate, never can go further.

On some systems BASE64 seems to not working.
Try the following.
Open autentification.php and delete all line and add just ACTIVATION = 1;
Then in ADMIN folder create an Apache autentification with .htaccess
or other folder based access method.