Not sure what is not working when you try to login to yahoo!
It will be helpful to solve the problem if you can elaborate more on the problem in steps.
Still following steps should help you getting automatic login to yahoo :
Step 1: Go to "Tools->Preferences->IE Integration", make sure "Internet Explorer Integration" check box is selected.
Step 2: Select "Interactive : request data in dialog " radio button.
Step 3: Browse to "
http://mail.yahoo.com/", it will bring up a dialog in which you can enter login details and can select "Perform automatic login to this Web page", so next time when you visit to this url, login fields will be filled for you.
So if you can explain problem in detail, we may be able to help you better. It's a good application and lot's of people are using it. Please give us a chance to resolve the problem you are facing.
For "Master Password" failure, please give us some example, to test out and see the problem. Any snapshot of error will be help too.