I've had that in the past, thought it meant the Search function was "busy" or on use by a few members at that time?
Usually I wait a few minutes and try again and it works.
Its been like it since last night for me. Doesnt matter what i try just not having it.
Only way i found is going to index like you said and clicking on each sub forum and then having to go back from there, getting a bit tedious now though.
Cant do any searches from anywhere at all.... its like its dropped off a cliff. As tintin says, for 2 days now, and I'm not getting any e-mail notifications (yes I've checked my settings)