Need MySQL configuration options like 'first time' When I installed MySQL-5.1.49-win32 for the first time I got a window asking 'root password' and 'confirm' in 'mysql server instance configuration wizard'.

Now I uninstall the software and install the same setup. It always asks me for the current root password even after I remove the 'instance' then configure it.

Seems a file containing password is left behind after uninstallation.

I remember my old password and am able to set new root password to anything of my choice. But I don't want MySQL to ask me for the old password while configuring.
Encrypted passwords are stored in a table.  You apparently kept the data while updating the software?  So the pwd was still there.

You could change the password to nothing.
You could start mysql "skipping the grant tables.
You could live with the brief inconvenience.
You should consider moving forward to 5.5, 5.6, 5.7.  (With the same pwd issues.)