Sure you ran it right? Works fine for me, and it won't only work for some people and not others. If not, just delete the row where the name is _password.
Yeah it says 0 rows edited. So the query didn't really change anything.
In what table do I find that row?
^ required table name is mybb_pluginuploader (assuming that database table prefix is mybb)
Is there even a row there where the name is set to _password? If the query didn't affect any rows then you must not have a password set at all, but if that was the case it would prompt you to set one.
This is now resolved. Thank you both.