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replacing (deleting and reuploading) the local.php file didn't work for me.
Although I did fix it. All of my permissions were wrong, public_html/cache, public_html/templates_c, and public_html/uploads I had to make them writable again.
The strangest thing in my situation is that this module and all other modules were working previous to this problem.
I don't know how my permissions got reset, but that was my problem with this error.
And word.idx was found in cache/word.idx