One user can’t login. Strange problem!

We've migrated from 6.xx to 7.6.

After several tests, etc. etc. everything seemed fine. We opened the new forum and everything is normal with all the users loging in as normal.

All.... but one (there's always one :)

When he tries to login the message "user or pwd error"  appears. Of course I already changed its password and tried to login with its user. No way! He also can't use the "Lost password" feature...

I'm out of solutions. I've checked the user in the db and everything seems OK. What can be happening here. The user name is
DREAD[]MAUZAO and he could always use the 6.4x version...

I also imagined that, but that user registered a new username
DREA[]somethingelse and it worked...

Strange....!

when he registered with [] they were probably transformed to nothing or something else..

tell the user to use something else.. he should not use other signs than numbers and letters a-z.. then youre sure it will work.. he might use some special signs, but not []<>' and ".. there might be other signs too..

all special charachters are transformed to ASCII or something like that..

that means your user has to login with &#091;([) and &#093;(])