I am a long time user of yahoo, and most of the time it is a great service, but it can be buggy at times.
Whenever I get an error when trying to load my yahoo messenger or my yahoo mail page I do this:
1. close out yahoo and all internet browsers
2. Run a program called CCleaner (get it
here)
3. install the program and Press Analyze
4. now press "Run Cleaner"
5. Select Registry tab on Left side of screen
6. Select scan for issues
7. Select Fix issues (run this until no issues are found)
you should now be able to succesfully connect to your yahoo mail.