Sometimes you can't access your store.yahoo.com login due to Yahoo Store server maintenance issues. It's only happened to me maybe 8 or 9 times in the past 5 years, but when it does, it's EXTREMELY FRUSTRATING!
"Secret" Manager/Editor backdoor login: Use http://edit.store.yahoo.com/RT/EDITOR.YOUR-ACCOUNT-GOES-HERE/cgi-bin/mgr-startup?ADVANCED
Replace YOUR-ACCOUNT-GOES-HERE with your account name. Then click on INDEX and the MANAGER button should work.