Error code 40402

[Solution # 1]
You will need to go to your Yahoo! Email Account and delete the contact's name there first.

1. Click Contacts from in the toolboxt to open.
2. Go to the contact you wish to remove and click the box next to it.
3. Go to the top of the list and click the Delete button.

Go to Messenger. When your list of Contacts opens, right click next to the name you wish to remove and select Delete from the drop down menu. The contact will be removed here also.
Error Code 40402 pops up when trying to remove a name while in your Yahoo Instant Messenger list first.

[Solution # 2]
Quit the program, then delete the contents of the “Cache”-folder located here:
c:/program files/Yahoo/Messenger/Cache


That usually solves a lot of problems, that occur all of a sudden. Try that and see if it works

[Solution # 3]
most probably a registry error - if you do not have a registry cleaner try downloading the free version of ccleaner from filehippo
once its downloaded select 'registry' from toolbar on left hand side and run 'scan for issues' followed by 'fix selected errors' if errors are detected
use microsoft 'one care' for further check


Hope they could help you
Good luck