I used to synch my 9700 with Yahoo mail, calendar and everything without any problem with the version 5 of the BB Desktop manager.
Since 3 weeks, it doesn't work: the error message is: the connection with the yahoo server is lost ( while synchronisation)

Is someone knows what happened with yahoo...

Alain

Sometimes it's as simple as opening the SetUp app and verifying security settings for your Yahoo email account.

Other times you need to delete the Yahoo email account from your BlackBerry and re-add it. I had this problem with GMail and calendar/address book sync. Once I deleted/re-added the GMail account I was prompted to verify security settings through Update app and that was all it took to restore wireless syncing.