Spotlight reports "Indexing and searching disabled" in Lion Lion keeps "losing track" of Spotlight information. Directories and Applications disappear, full text searches stop working, etc. I seem to need to re-index it once a week or so. 

However, now it appears to not work at all.

Running 

sudo mdutil -i on /


from the Terminal I get a message

"Indexing and searching disabled."


I have tried trashing preference files, deleting the whole V100 folder, repairing permssions, etc but Spotlight still thinks indexing is turned off on my entire Volume (Yes have added/deleted whole disk from Spotlight's privacy preferences").

In the console I have quite a few errors that look like this

mds: (Error) Server: Disabled store registered for scope "/Applications"


However, I do not know how to tell it to re-enable that scope as mdutil gives an error when I try to turn on indexing and gives an error when I try to delete the index 

EDIT: I reinstalled Lion. It did not fix the problem(s) :(
I had the exact same problem, with all solutions above failing identically. Then I reexamined the directory listing for / and found a hidden file .metadata_never_index in the root directory. I removed this file and was able to turn spotlight on again with 
mdutil -i on /.

mds is now reindexing the hard disk, all looks good for now.