Can't update due to validation limitation.

I've got an odd case where the certain models doesn't want to either update and/or create a new one. The problem, as I later found out, was due to validation errors (which is great, actually) except for some reason, <%= error_messages_for 'some_model' %> doesn't print anything. This is problematic, because as it turns out, one of my user models won't update because I have to provide a new password, each time.

Long story short, I have two problems:

error_messages_for method doesn't seem to print anything. Does this have to do with how I'm bringing up the code in my controller? A typical update method in my controllers look like this:

The second problem is how do I update only portions of the model (preferably some method that accepts an :except parameter) given by the text field in the view forms that's supposed to update the model. I'm currently using the method update_attributes(params[:user]), and I DON'T want it to update the password if the password field is empty, which this method seems to be doing.

I forgot to mention that I want the method to update portions of the Model while, at the same time, passes through the validation filter. I also realized half the problem also lies on how some parameters are required in the user model. By using singular update method, do I have to pass through those validation filters as well?